I have built two buildings that might help. Both are really old (and a little embarassing), but oh well.
This one and
this one
The burning church was originally this
MOC (warning: the link is to a thumbnail, the actual pic is old and big) and I was tearing it apart I decided to build a diorama around it. The horse stable was supposed to be a ruined building that was rebuilt. For both of them, I built an actual building and then tore it down to get the right effect. I have tried building ruins without doing that and they haven't turned out very well.
Hope this helps,
Josh
PS. I just remembered one other that I built...
this one. Its a bit better and the things I said above, apply to this MOC too. Except that I did build the causeway in a ruined state originally, but the building was built whole first.