Did you check the amount for liquidated damages in the contract. Often its just $250 per week which is not sufficient to cover most people's cost.

Get an independent building inspector ASAP so that there is a written report and then you need to address this with the builder in writing.
An offset can be used but…

Hi
I entered into a contract to have a house built in my back yard. The builder is at lock up stage and has exceeded the contract date. He is in…