Conformal features in CAD

Hi all.

First post! Looking for some help.

I have a architectural floor plan (a .stl file) of a villa with a lot of furniture. The furniture is extremely detailed (e.g. the cabinet has drawers and partitions as a part of the CAD). However, for my purposes, I don't need that level of detail because when I 3D print the design, the cabinet will be closed. So ideally, just the outer details of the cabinet is enough for me.

What I am looking for is essentially a way to be able to only get the outermost details of the floor plan and discard any internal features. IS there a way for me to extract a surface which conforms to the outer surface of the floor plan? I am well versed with FreeCAD, CATIA and Magics. Fair level of comfort with Meshlab and OpenSCAD.

Thanks