What open book means
On an open-book (sometimes called cost-plus) contract, you pay the real cost of the work: every trade, every supplier and every material, at the price we actually pay. On top of that sits the builder's fee, agreed in writing before construction starts.
Nothing is hidden inside a lump sum. If the framing package comes in under the estimate, the saving is yours. If tile costs more than planned, you see why, and you decide what to do about it before it is ordered.
The builder's fee, agreed up front
The fee covers running the job: supervision, scheduling, insurance, the office and the builder's margin. It is set at the start, either as a percentage of cost or as a fixed amount, and it is written into the contract.
Ask any builder exactly how their fee is calculated and what it includes. A clear answer to that one question tells you a great deal about how the rest of the project will run.
What a monthly cost report shows
Every month you receive a report that lists the budget for each part of the house, what has been spent so far, what is committed and what is left. Behind each line are the invoices themselves, which you can ask to see at any time.
Changes are tracked the same way. Each one is priced and approved in writing before it is built, and the report shows its effect on the total. By the end of the build there are no surprises, because you have watched every number move.
Open book vs. fixed price
A fixed-price contract can feel safer, but a builder taking on all the risk has to price that risk in. The cushion is usually buried inside the number, and you pay it whether or not anything goes wrong.
Fixed price also tends to turn every unclear detail into a change order. Open book lets you make decisions as the house takes shape, with real prices in front of you, which suits a custom home where many choices are still open when construction begins.
Questions to ask any builder
Can I see a sample monthly cost report? How is your fee calculated, and what does it include? Will I see the trade and supplier invoices? How are changes priced and approved? Who reviews the budget with me each month?
If the answers come easily, and in writing, you are talking to a builder who is comfortable being seen into. That is the builder you want.