As my building is supposed to be from the Middle East, it looks quite natural with thick walls. For this reason, plus the fact that the building is part of a static creche display, I don't need to make it from sturdier materials. To make simple buildings like this cut simple pieces from foam, cutting simple window shapes where you want light to be visible for a nativity building. If you want your building to be more than a backdrop in a village, you can design it with an open front so you can set a scene inside. I designed my building to have an open back so that I can set it over a light for a Christmas display. My building only needs a front wall and two side walls. The back will never be on view.
Styrofoam bead board tends to show the bead surface on cut or crumbled edges. You can choose to use this to highlight crumbling corners on the building.
For my domed building I cut the walls so the front wall will cover the edges of the side walls, and the walls will extend out slightly farther than the dome. My building has small arched windows as I want to make it resemble buildings from an existing porcelain nativity set in my collection.
Once the building walls have been cut out, apply a coat of artist's gesso or Rosco Foamcoat (or you can use unsanded grout) to protect the foam surface and add strength to the building. If you are using gesso you may need two to three coats depending on the type of foam you are using.