When I build I usually start with a room. Then I add other rooms as I work out what my sim needs. If I try to build a great house from scratch I get bored and abandon it. So building is usually part of a game for me. If a house turns out to be useful and suitable for many different sims I'll save it to my library and re-use it. I tend to try to avoid building anything from scratch and will reuse what I already have if possible. Even if I have built something special to fit on a hilly lot and then want to add it to a flat lot. That can give me some landscaping drama that can take days for me to sort out but I'd rather do that than try to build it again.