It started off as a sheet of Elmer's foam core board. I peeled the paper off of one side so I could give it some texture. That was rather a pain. Maybe I will try wetting the paper with water (or Windex) next time as others suggest.
Then I used an el cheapo wire brush assortment to give a rough, vaguely swirly texture to the walls in a effort to make it look like wattle and daub. I may even try to carve in some detail of wattle poking through.
Next up was cutting up some coffee stirrers to use as wood beams. I worry these may be a bit to wide to be realistic, but that's why we do things like test walls, right?
The building I'm basing this on doesn't have a door on the end wall, but again, this being a test I might as well test doors too. This one was made by scribing the foam with a mechanical pencil. The horizontal boards on the door are cut from business card. The door jams are an attempt to cut down the too-wide coffee stirrers. Kind of hard to control how wide they will be when cutting with the grain, but I think that adds to their Dark Age charm.
The whole door was cut out from the wall and then recessed slightly. Probably not necessary with the wood frame but again: test, test, test!