Here’s a paper model of an urban gunstore. It would be useful in any number of modern urban warfare games.
Paper Models
Urban Auto Electronics Shop Paper Model
This paper model is an appropriately grungy model of an auto electronics store.
Industrial Science Fiction Building Modules
Toposolatario offers IKubes — paper models of mass produced building modules from the distant future. You can quickly make a few dozen of these in different colors and decorations to completely fill a game table.
Roman Villa Paper Model
This free paper model of a Roman villa seems to be somewhere between 15mm and 20mm size. You could scale it on your printer, though to make it work in other sizes.
Iroquois Longhouse Paper Model
For your colonial America miniature wargames, here’s a paper model of an Iroquois longhouse. It’s a pdf file and in black and white, so you’ll have to color it yourself. Watercolors should do a good job with this.