One of the oddities of this building that the gauge of the roof and walls is much heavier metal than anything else I have xperiences.
I think the use of heavier gauge steel of the roof and walls that the OP notes, further points to this being homemade by a skilled craftsman. The train companies of the prewar era tended to use lighter gauge metal, which was easier to work with and less expensive. A heavier gauge of steel would have been more costly (which would lower profit) and be more difficult to work with.
I think that looking at the construction (from the inside of the building) would provide more information. I did note that there appears to be a rivet or screw at the center of each end wall (between the upper and lower windows), which may be attached to some sort of bracket inside.