Hmm... looks like you actually want Section Planes, or Slices. (Unfolding would be too much to expect for an Interior Design program.) It probably would be a nice addition to SH3D, but perhaps not too many users.

You can try exporting to Freecad . See this page: Yorik's guest blog - around halfway down the page. It's not a very easy program to learn.

Blender and Wings3d - the other opensource programs - also have ways to slice the object. I haven't tried this in any of the programs yet, though.

Sorry for posting this in the "Wishlist".