Check out the Links tab at the upper right of the page. There are many sites listed there with free models and models for sale. Many different subjects.
Here is a site that lists a lot of sites to get models. Some of the links might not be working, though.
Free Paper Toys, Paper Models and Paper Crafts at ss42.com
There is a section on buildings there.
Schreiber-Bogen is a publisher that has a lot of buildings. The skill level for those range from beginner to advanced. There are a few build threads for S-B buildings here on Paper Modelers.
