# The Custom Home Design Phase: How to Get a Real Number Before You Sign
TL;DR — The custom home design phase is where a real, buildable number gets built. It runs 6–12 weeks, costs 10–15% of your total build budget, and produces plans, engineering, and every material selection — the three inputs that make “fixed price” mean something. Below: what happens each week, what it costs, and why any builder who quotes without doing it is guessing.
The custom home design phase is the pre-construction stretch where a builder turns your idea into a set of drawings, engineering, and specifications complete enough that a number on the last page is actually true. Depending on the size and site, it runs six to twelve weeks and costs somewhere between 10% and 15% of the total build budget. This post covers what happens week by week, what the design phase costs, what it produces, and why the number a builder quotes without doing it isn’t a real number at all.
I’m Bryce Swager. I run [SwagerBuilds](
https://swagerbuilds.com/) — a custom home builder covering Eastern Idaho, Teton Valley, and Western Wyoming. I do a paid design phase before I sign a fixed-price contract on any build. That’s not standard in this market. It’s the whole reason my pricing holds up.
## What “design phase” actually means
The design phase is not the pretty renderings a spec builder shows you at the tradeshow booth. It’s not a 3D flythrough. It’s not a Pinterest board.
The design phase is the engineered, scoped, priced set of documents that let a real builder quote a real number. It’s boring paperwork. It’s stamps from a structural engineer. It’s a spreadsheet with a Kohler faucet model number in a specific finish. It’s a snow-load calculation for the pitch of the roof you picked, in the specific climate zone the house is going to sit in.
There’s a difference between an architect’s design work and a builder’s design phase. An architect’s job is to draw the house — the shape, the light, the feel. That’s real, valuable work. But an architect’s drawings, by themselves, don’t tell you what the house costs to build. They tell you what to build, not what to buy or how the framer prices the roof structure.
A builder’s design phase sits on top of architectural drawings and answers the question the drawings can’t: how much. It’s the phase where the drawings become buildable, and the buildable becomes priced. My [honest guide to custom home pricing](
https://swagerbuilds.com/honest-guide/) covers the longer version of why this distinction matters.
## The six things the design phase produces
A design phase is complete when six things exist:
**1. Buildable architectural plans.** Not just a floor plan. Every wall section, every elevation, every detail — how the deck ledger flashes, how the window sits in a thick-wall assembly, where the roof pitch changes and how it terminates. If the drawing set doesn’t show it, a sub-contractor will guess it. Guessing costs money in change orders.
**2. Structural engineering stamps.** Foundation design, framing plan, beam sizing, shear-wall layout. Snow-load calculations for the actual site — a 60 psf ground snow load in Teton Valley is a very different beam than a 40 psf load in Ammon. Framing without a stamp is a bet, not a plan.
**3. Complete material selections.** Every SKU, every finish, every fixture, every appliance model number, every knob and hinge and switch plate. This is the part most homeowners underestimate. “We’ll pick tile later” is how a $1.4M budget becomes $1.65M. A real design phase forces the decisions up front, when they can still move on paper instead of on site.
**4. Site work assessment.** Soils testing, drainage plan, utility routing — how power gets to the house, where the meter sits, whether you’re on well and septic and what those add. On a Teton Valley lot with a long driveway and a shallow water table, site work can be a six-figure line item on its own.
**5. Sub-contractor bid packages.** Each trade — foundation, framing, plumbing, electrical, HVAC, roofing, drywall, tile, cabinets, flooring — gets a scoped package with the drawings and specs for their piece. They quote to that package, not to a napkin. When ten trades all quote to the same document, the final number is built from ten hard numbers, not one builder’s best guess.
**6. The final fixed-price number.** The sum of the above, plus a contingency for the unknowns that always exist — bad soils, a code update mid-permit, weather delays. That’s the number that goes on the contract.
You can’t get to a real number without those six inputs. Anyone who says otherwise is either guessing or planning to make up the difference in change orders later.
## Week by week — what a SwagerBuilds design phase looks like
Here’s how the twelve weeks typically run on a $1.5M Rigby-area build. Bigger jobs — a $3M mountain build in Alta or Wilson — often stretch to fourteen or twenty weeks because the engineering is heavier and the selections are more custom. Smaller remodels run tighter.
**Weeks 1–2: Programming.** What are you building, for who, on what land, at what standard? I walk the lot with the client. We talk square footage, room count, how the family lives, where the sun rises, what the neighbor’s driveway does to your view. I take notes. I don’t draw anything yet.
**Weeks 3–5: Schematic design.** The architect drafts a floor plan and massing — the shape of the house on the site. We iterate. A wall moves. A window grows. The garage rotates ninety degrees to solve a driveway problem. By the end of week five, the footprint is locked.
**Weeks 6–7: Detailed design.** Every wall gets a section. Every window gets a size and a manufacturer. Every roof plane gets a pitch, a material, and a snow retention plan. Drawings go from “concept” to “buildable.”
**Weeks 8–9: Engineering and selections.** The structural engineer runs the numbers and stamps the plans. In parallel, the client and I pick every finish. Not “white oak floors” — a specific white oak floor from a specific mill in a specific width and finish, with a per-square-foot price. Not “quartz counters” — the exact slab, the exact edge profile.
**Weeks 10–11: Bid packages out to subs.** Each trade gets a scoped package and two weeks to quote it. I follow up in writing so no one later claims the scope wasn’t clear.
**Week 12: Final number, contract, permit.** I sit down with the client with the actual number. If they want to bring it down — swap a countertop, simplify a roof detail — we do that now, before signature. Once we agree, the contract signs and the permit application goes to the county.
That’s the version I run. Other builders run different variations. But the timeline shape — programming, schematic, detailed, engineering, selections, bids, final number — is roughly universal for any builder doing real design work.
## What the design phase costs
The design phase costs 10–15% of the total build budget.
On a $1M build, that’s $100K–$150K. On a $3M Teton Valley build, $300K–$450K. It scales with complexity. A simple two-story on a flat lot with a spec-grade material set lands at the low end. A four-level mountain build with a walk-out basement, structural steel, custom cabinets, and a geotech-required foundation lands at the high end.
Where does the money go?
– Architect fees (usually the largest single line)
– Structural engineer (foundation, framing, snow load)
– Geotech testing if the site requires it
– Interior designer, if the client brings one in
– My time coordinating the above, running selections, running the bid process, and building the final number
Important: **the design phase is paid separately from the build contract.** You are not paying a retainer against a construction budget. You are paying for design work. You get the drawings, the engineering, and the specifications regardless of whether you build with me.
Fair question: **what happens if you walk?** If you go through the design phase and decide not to build — or build with a different contractor — the money doesn’t come back. The work is done. The engineer stamped the plans. The subs bid the packages. Nobody worked for free. I say that up front, on paper, before a check is written.
## Why “fixed price” without a design phase is a lie
A quote based on a floor plan sketch and a written scope is not a fixed price. It’s a guess dressed up in a contract.
Here’s how it works. A builder wants your job. He gives you a number — say $850,000 for a 3,000-square-foot Rigby build — with a stack of “allowances” baked in. $8,000 for cabinets. $5,000 for lighting. $12,000 for tile. $6,000 for appliances.
Nobody has picked cabinets. Nobody has picked lighting. Those numbers are placeholders — the builder had to put something in to hand you a total. When you go to pick cabinets, the ones you want cost $28,000. You get a change order for $20,000. Same story on lighting. Same story on tile. Same story on twenty other allowance lines.
By the time the house is done, your $850K contract has become $1.15M in signed change orders. The builder — who quoted the lowest number in your bid stack to win the job — is now making his real margin on the changes. You can’t fight him. The walls are up. You’ve paid a big deposit. You’re captive.
That’s the mechanic behind every “we agreed on $800K, ended up at $1.2M” story your neighbor tells you. It isn’t fraud. It’s built into the contract. The builder didn’t lie. He quoted a number that was never real, and the change orders were the plan.
The design phase is the fix. When every allowance is a selection with a SKU and a price, there is nothing to change-order. When every trade has quoted to a scoped package, there is nothing to renegotiate. The number on the contract is the number you pay.
## When cost-plus is honest, and when it’s a trap
Cost-plus — where you pay the actual cost of the build plus a percentage fee to the builder — is a legitimate contract in specific situations. It’s a trap in most of the others. This series covers it in depth in the next post, but the design-phase lens is useful here.
Cost-plus **with** a paid design phase is a weird combo. If the whole point of a design phase is to produce a fixed number, why sign an open-book contract that bills you whatever the true cost turns out to be? There are honest reasons — genuinely unknown site conditions, a client who wants to change scope mid-build — but they’re the exception.
Cost-plus **without** a design phase is where the trouble lives. This is the “we’ll figure it out as we go” contract. You are writing blank checks. Every decision made on site is billable at cost plus the fee. Every mistake, every rework, every over-order — you pay for it. The builder has no incentive to run a tight job, because a loose job pays him more.
Both contract types can be honest. Neither is honest without a design phase behind it. Posts 3 and 4 in this series cover the full teardowns.
## The design phase as a filter — what happens if you skip it
I’ve watched clients skip the design phase because a competing builder promised a faster start and a lower quote. The industry data on the outcome is consistent:
– **Change orders on unpriced builds average 15–35% of contract value.** On builds with a real design phase behind them, change orders average 2–5%. That’s the difference between a $150K overrun and a $30K one on a $1M build.
– **Timeline overruns on unpriced builds average four to seven months.** On priced builds, they’re closer to two to six weeks — and most of that is weather, not scope.
– **You lose your negotiating position the moment construction starts.** The walls are up. The money is spent. You aren’t going to fire your builder mid-frame — the cost of switching is worse than the cost of finishing. This is why the builder who quoted low needs to keep costs invisible until the site is committed. The design phase is what keeps that from happening.
This isn’t hypothetical. It’s the pattern behind almost every “our custom home was a nightmare” story in the local market. Skipping the design phase is how the nightmare starts.
## When it makes sense to skip the design phase
A few real cases where a paid design phase is overkill:
– A small, tightly-scoped remodel — kitchen refresh, bathroom rebuild — where the scope is truly contained and the finishes are picked before the contract.
– Cost-plus at close-friend or family rates, where both sides genuinely understand the exposure and the builder isn’t trying to grow margin on changes.
– A repeat build using a plan set the builder has already built two or three times, where selections and engineering are largely locked before you walk in the door.
Outside of those, skipping the design phase on a $1M–$5M custom build is how you end up in a lawsuit. This is why I publish floor pricing on the site — $285–$500 per square foot for Rigby, Idaho Falls, and Ammon, and $550–$1,200 per square foot for [Teton Valley builds](
https://swagerbuilds.com/cost-to-build-custom-home-teton-valley-2026/). The number filters out clients shopping for the lowest bidder — usually the same client who ends up on the wrong end of a change-order contract with someone else. I’d rather lose that client early than fight them at month nine.
## FAQ
**How much does the custom home design phase cost?**
Between 10% and 15% of your total build budget. On a $1M build, that’s $100K–$150K. On a $3M mountain build in Teton Valley or Jackson, expect $300K–$450K. The percentage runs higher on complex sites, lower on simple lots.
**How long does the design phase take?**
Six to twelve weeks for a straightforward Eastern Idaho build. Fourteen to twenty weeks for a larger custom mountain home with heavier engineering, custom cabinetry, and a longer selections list. The timeline stretches with complexity, not with builder speed.
**Do I own the plans at the end of the design phase?**
You use the plans for your build — permit them, build them, live in them. I retain the right to sell those plans as spec plans to future clients. That’s how I keep the design phase cost reasonable and how great designs get built more than once. If you want exclusive rights to the plans, we can negotiate that separately at kickoff — it costs more. Whatever we agree to is in writing before we start.
**What if I change my mind mid-design?**
That’s the point of doing the design phase before construction. Every change made during design is cheap — pencil on paper. Every change made after construction starts is expensive — labor, materials, and rework. This is the phase to change your mind in.
**Can I get plans without hiring the builder for construction?**
Yes. A paid design phase produces a complete document set any competent contractor can build from. If you take my design set to another builder, that builder can quote it. That’s why I don’t discount the design phase — the work stands on its own.
**What if my architect already did plans — do I still need a builder-led design phase?**
Usually yes. Architectural plans, even good ones, rarely include the selection detail, sub bid scoping, and priced-out material list a fixed-price contract needs. A builder-led design phase sits on top of the architectural set and adds the buildable, priced layer. If your architect’s set already has all six things listed above, you may be closer to done than you think. Send it over and I’ll tell you honestly.
## Related posts in this series
This is post 1 of a 6-part series on how custom home builders actually price work — and how to tell an honest contract from one designed to grow on you.
1. **The Custom Home Design Phase: How to Get a Real Number Before You Sign** (this post)
2. Cost-Plus vs Fixed-Price — Which One Are You Actually Signing? — [Read →](
https://swagerbuilds.com/cost-plus-vs-fixed-price-custom-home-contract/)
3. Cost-Plus Contracts — A Working Builder’s Honest Take — [Read →](
https://swagerbuilds.com/cost-plus-custom-home-contract-honest-guide/)
4. Fixed-Price — What Real Fixed-Price Requires — [Read →](
https://swagerbuilds.com/real-fixed-price-custom-home-what-it-requires/)
5. GMP (Guaranteed Maximum Price) — When It’s the Right Move — [Read →](
https://swagerbuilds.com/gmp-guaranteed-maximum-price-custom-home/)
6. Time & Materials — When It Makes Sense and When It’s a Trap — [Read →](
https://swagerbuilds.com/time-and-materials-custom-home-contract/)
## If you’re planning a build
The one question to ask any builder before you sign anything: **”Do you do a paid design phase before you quote, and can you show me the deliverables from your last three clients?”**
If the answer is no, you are not getting a real number. You are getting a marketing number, and the change orders are the plan.
If you’re planning a build in Eastern Idaho, [Teton Valley, or Driggs](
https://swagerbuilds.com/driggs-idaho-custom-home-builder/), or the mountain side around Jackson, Wilson, and Alta — and you want a builder who quotes what he can actually deliver — [get in touch](
https://swagerbuilds.com/contact/). I’ll tell you honestly whether your project is a fit for a paid design phase or whether you’re better off with a different approach.
That answer is free. The design phase, when it starts, isn’t.
