In order to use less filament, the apartment can be printed in two separate parts; the main body of the apartment and the roof. If printed this way, the interior of the apartment will be hollow.
The files apartment-half-roof and apartment-half-hollow should be printed together if you only want to print one apartment half. The files apartment-roof and apartment-hollow should be printed together if you want the full apartment.
If you don't want to save on filament, you can print apartment-half-solid or apartment-solid to print out half of an apartment or a full apartment.
This model definitely needs supports to print. For strength, there should be about 0.4mm of walls and at least 15% infill.