Here’s a paper model of a medieval watchtower in 1:140 scale. The site is in German and the babelfish that I used wasn’t very good in translating it, so I can’t tell you much more. 1:140 scale is probably not good for most miniature wargames, but you could easily scale them up when you print.
paper model
Paper Brick Building
Clifford Button of Paper Tiger Armanents offers a free 1/72 scale brick structure. It was inspired by a building in the Strand district in Galveston, Texas.
6mm Paper Vehicles
Germy’s World has some nice paper models for 6mm science fiction gaming. There are tanks, drop pods, a mega drop pod and a drop ship. These would be useful for Battletech, or Reaper’s CAV, or Games Workshop’s Epic 40K.
Modern and Sci Fi 6mm Buildings
Germ’s World has a large collection of paper models for wargames in 6mm scale. These would be useful for, say a BattleTech game, or maybe Epic 40k. There are hangars, moon bases, factories, space docks and middle east buildings.
Here’s an idea for a miniature wargaming scenario: During WWII, a group of US paratroopers, or British commandos are sent to destroy a V-2 rocket base. Of course, to do this, you’re going to need to add a model of a V-2 rocket to your terrain. This website has a free paper model of a V-2 rocket in 1/32 scale. You could easily rescale it on your computer.