I have made progress on my HO scale scratchbuilt paper model of FOS Scale Models' "Rust Rock Falls" main structure. The walls, roofs, doors, and windows (except cupolas) are paper. Stairs and platforms are stripwood and brass screen. I made mine a mirror image of the Fos design to fit the space on my layout. I will put the building on a base of rigid foam with a small dam and mill stream. I have a few details to add, then in goes on the base. I have not modeled the back walls since they won't be visible on the layout.
