On a general purchase contract there is the “loan contigency” clause. That states if for any reason you can not get financing that you should get your deposit back. If you can not appraise at the requested price you can not get financing therefor should be able get your deposit back or a lower price. Lenders will not allow you to buy a home that is not worht the asking price. They do not like people being upside down in there home. I am sure the contractor would not mind however tha bank would block financing in a case like that.
Now that is a general purchase contract, I am not sure how it may work on a new construction contract but I am sure there is a similar provision…