EASY FOUNDATIONS & WALLS ! (dial up pic. warning)

They are 1/8th." thick. Most of all the pictures you see are ho scale and a few are N. The light colored cottage that I used in the tutorial is actually O Scale. You just will need to experiment a little. Maybe lay them on there sides? then you would have 1/4" x 1/2" blocks. and if you look at the stairs in the PDF those are 11/2" x 1".
Remember that these can be sanded smooth or filed ti rough them up even more.