Overlaying Room Walls

[PBS]

Hi:
I want to be able to draw various rooms, and overlay the common walls
precisely. I can get them close, but not perfect. Is there a grid or snap
or other setting for the amount the cursor arrows move an object that will
permit me to more precisely move the rooms to align them?

Also, is there a way to adjust the "Wall thickness" of a room? I know how
on individual wall segments, but can't see how to on a room.

Thanks