Backing out of a custom built new construction

[Logan Pou]

A friend was saying they got approved for a house, but they cant lock in the final price because they have custom built it and its still under construction. so they cant lock it in until 2 months prior to signing and the price is continuing to go up. i was just curious if anyone could explain what would happen if the buyer needed to back out of a custom built new construction because of the price became too high ? I am also curious about if and how  the new interest rate hikes would affect the buyer in this situation ? Thanks so much for your time