On the official forums, someone has found a way to keep from crashing while building. Most of the crashes will not happen when you don't have an active family so you could start a new game and do all your building then save. Then save the lot and place in your active family gamefiles and it should be able to be saved without any worries.
For those of you who can't do this (dynasty & challenge players), it is recommended to wait at least 24 Sim hours before saving the game after building. This seems to reduce the amount of crashes after building according to all the things I read today.
