To set the thickness of your walls while you draw them or after they've been drawn, follow the instructions below.
Adjust walls while you draw:
Using either the wall or room drawing options, once you click on the grid and begin drawing, you'll see a menu pop up at the top of the screen where you can specify your intended wall thickness. This will change the thickness of all 4 walls when drawing a full room.
Adjust walls AFTER they are drawn:
V5.0
V4.0
Select the wall you want to adjust.
Visit the right hand panel and specify the thickness by dragging the dimension bar or typing in the digit.