I got these the other day off Amazon, they're listed as buildings for 28mm miniature wargaming but IMO they're closer to O scale in size.
This shows a Bachmann O scale figure and a 28mm figure from the Knuckleduster line of 28mm miniatures
Here's a MTH round roof boxcar as reference:
These are all MDF flat kits, the only difference is in the front wall and trim around the top of the front wall. The window and door trim are separate parts that I super glued in place and then painted, I left the exterior/interior walls unpainted cause I like them as they are. Only spots I put some super glue on were the tabs on the back wall where it attaches to the side walls to keep them in place, all other joints are fairly tight. The roof can be left unglued and taken off if you want to do interiors.
When ordering, you can choose what names you want to put on most of the buildings. The letters are also MDF and I super glued them in place after painting.
If you like the smell of burnt wood, these are for you ...maybe that's why I didn't paint mine!