My studio is a 12 x 16 metal cabin with four windows and a regular door. It has steel stud construction, bought unfinished inside, with a pressure treated floor. I added a porch by first cutting a bunch of wood to build a woodpile, then laid a chunk of plywood on that to form a table/work surface. With scrap lumber, I built a frame for the porch roof, and secured it to the underside of the studio's roof. Finally, I topped it off with a 10x12 Wal-mart tarp and anchored it with guy lines and tent stakes.
This set up has withstood years of storms in N.E. Georgia mountains.