How are you making the walls for your plans? The normal wall tool (from the little bit I've played around with DD3) seems to just make the walls one standard thickness and nothing more, no matter what value you give to the width.

Unless I'm doing something wrong and the above is incorrect, it looks as though you're using corridors as walls? I'm probably way off, so if someone could kindly explain how you make those walls and the little wall extension pieces and have them blend into the existing walls, I'd be greatly appreciative! Thanks!