Wanted to be able to upload a mesh (or more precisely, wanted to upload an STL) that had internal space (a building with just the walls) and have it be filled s

Wanted to be able to upload a mesh (or more precisely, wanted to upload an STL) that had internal space (a building with just the walls) and have it be filled so it's a solid object. That makes it easier to resize for printing, as you're not relying on wall thickness as the only structure. Is that any more clear?