World Works Games just came out with a great modular building set. They have always made some great quality terrain. With talent and determination, you can make more seamless buildings from wood and plaster, but WWG is worth giving a shot if you hate painting. One of my groups has always been very much against card-stock terrain, however, they have seen the value in card-stock buildings as temporary or support pieces.
Thoumont's TLX Building System
The beauty of this system is that you can make a temporary piece and tear it down to be reused in a different configuration later, without any degradation in the parts.
That said, Graffam also makes some great-looking buildings. However, apart from the ruins, none of the intact buildings currently have any interiors.
I would say that if you have both the time and the talent to build your own buildings from scratch, do it. But, don't discount card-stock if you don't have time to build and paint a beautiful scratch piece. There are great products available from many sources.