By the time the first wall comes down, the most consequential financial decision of your build-out has already been made, and it was not the budget. It was the contract structure — the choice among a fixed price, cost-plus, and a guaranteed maximum price. That choice determines who carries the risk of surprises, in which direction everyone's incentives lean, how much visibility you get into the real numbers, and what the arguments, when they come, will be about.
Most first-time owners inherit this decision — the GC proposes a structure, and it feels like part of the furniture. It is not. It is negotiable, it should fit the project rather than the contractor's habit, and understanding the three families takes twenty minutes. Here they are, in plain language. The standard forms from the American Institute of Architects in the US and the CCDC in Canada exist in versions for each structure; have a construction attorney review whichever one you sign.
Fixed price: certainty, purchased
The stipulated-sum or lump-sum contract is the one owners intuitively expect: one number for the defined scope. The contractor prices the drawings, adds their overhead, profit, and — importantly — a premium for the risk they are absorbing, and commits.
What you are buying is certainty, and you are genuinely buying it: risk transferred is risk priced in. If the job goes smoothly, the contractor keeps the premium; that is the fee for carrying your downside. The structure works best when the thing being priced actually exists — complete, coordinated construction documents. Price a fixed-sum contract from half-finished drawings and you get the worst of both worlds: a premium paid for certainty, plus a torrent of document-driven change orders where the drawings ran out, priced in the one-seller market we described in the change-order economy.
The incentive structure is worth saying out loud. Under a fixed price, every dollar the contractor saves is theirs. That funds efficiency, which is good, and it can fund quiet corner-cutting, which is not — the tension your architect's site visits and the inspection regime exist to police. And a fixed-price bid that comes in strangely below the others is not a gift; it is frequently a plan to bid the job back up through changes.
Cost-plus: transparency, with the meter running
The cost-plus (or time-and-materials) contract inverts the deal: you pay the actual, documented cost of labor, materials, and subcontracts, plus the contractor's fee — either a percentage or a fixed amount. Every invoice is open-book; you see what things really cost.
What you gain is flexibility and honesty of scope. There is no premium for risk, no incentive to inflate changes — a change is just more cost, transparently billed. For genuinely uncertain work — the old building nobody can price responsibly, the project starting before design finishes — cost-plus is often the only structure a good contractor will sign, and the only one you should want them to.
What you carry is the risk, all of it. The meter runs; surprises are yours; the final number is a forecast until the end. Two disciplines make cost-plus livable. First, a real owner-side reserve, sized and managed the way we argued in contingency is a plan. Second, real audit hygiene: defined billable rates, receipts behind every line, a monthly reconciliation you actually attend — the draw-review habits matter double here. And prefer a fixed fee over a percentage fee where you can get it: a percentage fee, structurally, pays the contractor more when the job costs more, and even honest people steer soft decisions along their incentives.
GMP: the hybrid everyone ends up discussing
The guaranteed maximum price sits between the two: cost-plus mechanics with a ceiling. You pay documented cost plus fee, open-book, but the contractor guarantees the total will not exceed the agreed maximum. Overruns past the ceiling are the contractor's problem; spending below it is savings.
Two clauses decide whether a GMP is a good deal, and both are negotiated, not standard. First, who keeps the savings when the job lands under the ceiling — the answer ranges from all-owner to all-contractor, with shared-savings splits common precisely because they align incentives. Second, what the guarantee actually covers: a GMP is only as strong as the scope documents behind it, and a ceiling full of exclusions, allowances, and assumptions is a ceiling with holes. Read the assumptions exhibit as carefully as the number. A GMP also carries the contractor's contingency inside the ceiling — ask how large it is and what happens to the unspent balance, because that answer is often worth real money.
GMP suits the project that needs to start before design fully lands but whose owner needs a bankable worst case — which is why lenders like it, and why larger hospitality projects, especially hotel work, so often end up here.
Choosing: three questions
Strip away the acronyms and the choice runs on three questions:
- How finished is the design? Finished drawings favor fixed price. Moving design favors cost-plus or GMP. Pricing certainty from uncertainty just buys expensive arguments.
- How much surprise does the building hold? New shell: fixed price prices well. Old bones, no as-builts, occupied neighbors: the risk premium a contractor must charge to fix-price that job may cost more than carrying the risk yourself, watched closely, under cost-plus.
- What does your money need? A lender or investor group that needs a worst-case number pushes you toward fixed price or GMP. An owner funding from cash flow who values every dollar of transparency may prefer open books and the meter.
And one meta-rule: the contract structure cannot compensate for the wrong contractor. A trustworthy GC under a loose structure beats an adversarial one under a tight structure when the comparison is made. The contract decides the incentives and the arguments; the humans decide the project. Pick the humans first, then pick the paper that fits the job — in that order, and with the attorney's hour budgeted before the signature, not after the first dispute.
The parts every structure shares
Whichever family you land in, a handful of provisions do heavy lifting and deserve the same attention as the price mechanism. Payment terms and retainage — the held-back percentage that funds your leverage through punch-list week. The schedule clause: whether the completion date is contractual, what extensions require, and what, if anything, happens when it is missed. The change-order pricing rules, agreed before signing, as we argued in the change-order piece. Insurance and indemnity requirements, matched against the coverage questions in our builders-risk guide. Termination provisions for both sides — unpleasant to negotiate, priceless twice a decade. And the dispute ladder: negotiation, then mediation, then arbitration or court, decided while everyone still likes each other. None of these varies with the acronym on the cover page, and any of them can matter more than the acronym does.
Structure follows design maturity, risk follows structure, and the arguments follow the risk. Choose accordingly.
The acronym on the cover page is the least of it; the allocation of surprise is the whole of it.