Once you've settled on a builder, the next question is how you'll contract with them — and most clients arrive at this fork with strong opinions and shaky information. Fixed-fee and cost-plus are the two main ways to structure a custom-home contract. Both are legitimate. Neither is a trick. What follows is a plain-spoken look at how each works, who carries which risk, and why the contract type matters far less than one thing that should be true regardless: a complete, written budget before ground breaks.
How fixed-fee works
In a fixed-fee — sometimes called fixed-price or lump-sum — contract, the builder commits to a single price to deliver an agreed scope of work. You know the number up front. If a subcontractor bids higher than expected, or lumber ticks up between contract and framing, that's the builder's problem to absorb, not a surprise on your invoice. In exchange for carrying that risk, the price includes a contingency — a cushion built into the number to cover the uncertainty the builder is taking on.
The appeal is obvious: certainty. You can take a fixed number to your lender, to your spouse, and to your own peace of mind. The trade-off is that you're paying for that certainty whether or not the risks materialize, and the builder, not you, captures any savings if the project runs smoother than priced.
How cost-plus works
In a cost-plus contract, you pay the actual cost of the work — materials, labor, subcontractors — plus the builder's fee, which is usually a percentage or a set amount on top. The defining feature is transparency: you see what everything actually costs, line by line, because you're paying it directly. If prices come in low, you keep the savings. If they come in high, you cover the difference.
The appeal here is openness and the potential to finish below a fixed-fee number when things go well. The trade-off is that the final total isn't guaranteed at signing — it's an informed estimate that resolves into a real number as the work happens.
Who carries the risk
Strip away the jargon and the whole comparison comes down to one question: who absorbs the difference between the estimate and reality?
- Fixed-fee: the builder carries the price risk. You pay for that protection through the contingency built into the number.
- Cost-plus: the client carries the price risk. You pay actual costs, so you're exposed to swings — but you're never paying for a cushion you didn't need.
There's no free lunch in either direction. Fixed-fee trades a margin for certainty; cost-plus trades certainty for transparency. Honest builders price both fairly; the structure just decides where the risk lands.
Transparency and the role of allowances
Cost-plus is transparent by design — you're looking at the real invoices. Fixed-fee can be every bit as transparent, but only if it's built on a detailed, itemized budget rather than a single round number. The mechanism that connects the two is the allowance.
An allowance is a placeholder for a decision you haven't made yet — countertops, lighting, plumbing fixtures, flooring. Generous, realistic allowances mean the contract total is honest, because the placeholders reflect what those choices actually cost at today's prices. Thin allowances make any quote — fixed or cost-plus — look better today and grow later, when you make selections that blow past the placeholder. Whichever contract you choose, the question to ask is the same: what does each allowance actually buy?
Where each one makes sense
Neither contract is universally better; they fit different temperaments and different projects.
Fixed-fee tends to suit you if…
You value a known number above all else, you're financing to a firm budget, you're building from out of state and want certainty without watching every invoice, or your design and selections are largely settled before contract so the scope is well defined. The more nailed-down the plan, the more accurately a builder can price it, and the smaller the contingency needs to be.
Cost-plus tends to suit you if…
You want to see every dollar, you're comfortable with some variability in exchange for that visibility, you expect your selections to evolve as the house takes shape, or the project has unusual scope where a fair fixed price would carry a large contingency you'd rather not pre-pay. Transparency-minded clients often prefer it precisely because nothing is hidden.
The part that matters more than the contract
Here's the thing the industry doesn't say loudly enough: the contract type is not what determines whether your project goes well. The completeness of the budget before ground breaks is. A vague fixed price and a vague cost-plus estimate both end the same way — in change orders, tension, and a final number nobody saw coming. A complete budget, built on real selections and realistic allowances, protects you under either structure.
That's why, at Walnut & Stone, we offer both fixed-fee and cost-plus and let the client choose — and either way, every selection and allowance is settled in writing and the full budget is complete before we break ground. That pre-construction budget isn't a contract type. It's a commitment we make on every project, part of what we call the Walnut & Stone Standard. Choose the structure that fits how you want to carry risk; the certainty comes from the budget, not the label on the agreement.
How to decide
Start with one honest question about yourself: do you sleep better with a fixed number, or with full visibility into every cost? That answer points you toward fixed-fee or cost-plus. Then, whichever way you lean, hold any builder to the same standard — a detailed, itemized budget with realistic allowances, in writing, before anyone moves dirt. If a builder can't or won't produce that, the contract type is the least of your concerns.
For more on how the dollars break down before you ever pick a contract, read what it really costs to build in Western North Carolina, and see how the budget fits into the whole build on the Standard.