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.
paper model
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.
Dr. Who Paper Miniatures
Crow’s Nest has a very nice set of paper Dr. Who Miniatures. I’m going to print them out and make a set for my eight year old Dalek Fan.
Paper Sloop Model
Warartisan is offering a free sample model of the Enterprise, one of the ships that fought on Lake Champlain in 1776. It’s part of paper model ships to go with the free Away Boarders rules for refighting naval battles on the Great Lakes in the 17th and 18th centuries.
15mm Paper American Civil War Wood and Stone Barns
At the Game Architect blog, you’ll find a good looking paper model of a 15mm American Civil War wood and stone barns. The models are in black and white, so you’ll have to apply your own coloring.