I like this idea. I would also suggest that if possible make it so that if the house hasn't been worked on in X amount of days that it can be destroyed. Another idea would be to give under construction houses a limited amount of time to be built. If the time expires people could A. Steal the supplies, or B. it would fall like a regular house.
Also destroying finished houses is a terrible idea, and they destroy themselves after a while.
You can finish other people's houses, I used to do it to get rid of some of the half finished ones, but it wasted too much of my resources.