Construction contractors working on the cutting edge of technology nearly always work on a cost-plus basis only. One kind of cost-plus contract stipulates the contractor' s profit as a fixed percentage of the contractor' s costs; the other kind stipulates a fixed amount of profit over and above costs. Under the first kind of contract, higher costs yield higher profits for the contractor
this is where one might expect final costs in excess of original cost estimates to be more common. Paradoxically, such cost overruns are actually more common if the contract is of the fixed-profit kind.
On any sizable construction project, the contractor bills the client monthly or quarterly, so any tendency for original cost estimates to be exceeded can be detected early.