I just posted are some very small paper house kits that can be used with S, O and O27 trains. These are inspired by those old “Village in a Bag kits from the 1960s. My original intention was for wargaming with 25 to 40mm figures. These houses have a very small footprint - 3” by 5" - and can be used to fill spacer, as background, or as cheap scenery. There is a “spare door” trick which changes the house from S to O.
http://www.thortrains.net/download25.html
Just download unzip and print - buildings are in PDF format.
Enjoy
Tho