I know the build price but not what the whole project will cost
The builder's figure is only one part of the decision; the plot, professional fees, connections, finance and contingency still have to fit the same pot.
What's happening?
A build price can look reassuring because it is a single number, but it is not the same as the cost of getting a finished home. Before work starts, money can also go on the plot, surveys, design, approvals, utility connections, insurance, finance and the work around the building. Some of those costs arrive before the builder is on site; others become visible only when a decision has already been made.
The useful question is not whether each allowance is exact today. It is whether every known cost has somewhere to sit, what is still an assumption, and how much room remains when those assumptions move. Putting the items on one checklist makes omissions and double-counting easier to spot before they become commitments.
The solution
Start by putting the parts outside the build price in one place.
If you would rather it were done for you, General Support is the service that does it.