Basic Level Editor Question

[TheIcyPickle]

This is probably Level Editor 101 here, and after a year on here I should know how to do this but, when dealing with dungeon walls with something like this:



(http://i.imgur.com/01OPkIn.png)

How do you allow the walls to form this essentially upside down L shape without the weird overlap.

Plus, the ways I have been doing it, when I finish a room, the room is un-even as if a wall was too short to finish the L shaped room.

Hopefully I'm being clear enough. I think you have to use wielders if I'm not mistaken.

Hopefully you guys know what I'm talking about!