Occasionally I get a bit scrap happy and accidentally knock down a wall that exposes the white void beyond the world. Happened yesterday, while trying to find a bit more space for power armor displays in the Mechanist's Lair (btw, there is a crapload of stuff just hanging in space down there where Bethesda couldn't be bothered to clean up after themselves.)
So, as an experiment, I pulled up a floor piece and stuck in an elevator, going DOWN into the void. Lo and behold I was able to take the elevator down and actually build a small room a couple stories down below the main room.
My question, then, is what are the limitations to expanding interior settlements out into the white? Is it simply a matter of adjusting the buildable area, and then building proper floors, walls and ceilings to hide the void?