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.
paper model
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.
Free Blood Bowl Pitch
The Gaming Corner has twenty different Blood Bowl pitch designs free for the downloading. Just print them out and glue the pieces to cardboard. The site also has Blood Bowl rosters and a quick reference sheet.