this rather generic listing of "Free Paper Models". When I started going down these interweb rabbit holes I was quickly overwhelmed by the sheer quantity of models available.
Now almost all of these are for buildings of various sizes and eras, but there is a little something for everyone. The only dead link I found (so far) was the one for WotC's free buildings.
Some of the sites listed have models for sale, but even then they have some free examples you can download.
The website isn't pretty, but it is a great "jumping off" point for looking for new paper buildings to use in your game.