I know paper buildings may not be for everyone, but I’ve been very impressed with Clever Models buildings.
http://clevermodels.squarespace.com/ I really hope they make some simplified designs that are scaled specifically for 28mm in the future.
In the meantime, I just wanted to show a quick example of how easy it is to scale their O Scale designs for tabletop gaming.

Typically it's the height of O scale that throws it off for 28mm, but with Clever Models paper buildings this is easily corrected by trimming about 3/8" to 1/2" off the bottom. This even drops the windows to a nice height. This trick won’t work for all their stuff but it should cover most of their simpler designs.
HAVE FUN!