They're made from 5mm cork sheet that I picked up at a model railway shop (although I did have a few scraps laying around from older projects. For these type of buildings cork has a nice texture.
I like this material because it's easy to work with. It's easy to cut and you can use just about any sort of glue with it. I used tacky PVA. You can sand it down to take away any rough edges and you can chip away little pieces to show the rough brickwork beneath. I did that with some walls that I made a while back (I'd add some pics but I can't find any).
As you can see the building is pretty basic. I used some off cuts to make the door frame and some of the windows have a bit of a pain. The wooden roof support things are just pieces of toothpicks that I cut in half and pushed into the cork. All very easy.
Oh yeah... The Roof! This is a piece of foam core. When it was all constructed I gave it a coat of PVA and sprinkled a touch of sand to give it some texture.Thin pieces of cork are pretty flexible if they have little bit of length to them. You can see where I made the arched door frame using this flexiness. I just did it one piece at a time. I glued and pinned the fist piece and when it was cured firmly in place I added the second piece and pined it. I came out okay as far as I'm concerned.
All painted with some cheap white acrylic with a very faint wash of sandiness on the roofs and floors.
P.S. The blue on the inside is from the blue marker that I used to mark out the windows and doors.
I won't use that pen again.