Cleaning out my parents' basement recently I discovered an HO building that I scratch built about 60 years ago (1963 or 64). Cardboard with brick paper glued on, various detail pieces from wire and balsa wood. It was a meat packing plant. Long gone from my memory, I was surprised to find it. I did not want to just toss such a survivor into the trash, so I decided to rebuild it as a background building flat for my O gauge layout. My "layout" is only in the planning and real estate acquisition stage (cleaning out my basement), so I set up a diorama to test out how various elements might look together.
I thought it was quite interesting how modeling techniques have evolved. Of course, as a high school student in the 1960's, my money was limited. So using cereal boxes and brick paper was standard procedure. I remember how sophisticated I thought my modeling was to actually use Walthers Goo as adhesive. And of course, Floquil paint, solvent based, for other colors. The loading door (not used in the flat) is Reefer Orange, as I recall. Sandpaper to simulate the roofing paper.
A background building flat is a good way to save a sentimental structure from decades ago.