I did my ceiling first, then went around the walls with "C" channel for the wall panels to fit up into. At the floor I used a "Z" channel backed with a piece of 2 X 2 for the wall panels to rest on. I used Metal Building Supply Co. in Piedmont, S.C. (
www.metalbuildingsupplyco.com) . Go to their website and get yourself a "buyers guide". It will give descriptions of the different trim pieces and is very educational. Even if you aren't close enough to use them, you will have some knowledge when you call your local supplier. Chip.