If you plan to do any welding, grinding, or using the hose, I think that the metal sheeting that is used on pole buildings would be great. I intend to use that when I get the $$$ to do mine. They have the panels in white and galvanized. They did tell me that white is better than galvanized when you will be welding, because of the reflections.
Our local supplier if
http://www.64metals.com/
Misled