Another source for boat sheds. Xtreme Shelters has a line of tough but inexpensive shelters. Saw one set up in Iowa during a 40 knot (cooold) wind earlier this month. They use galvanized tubing/pipe for the framing. The 20 x 10 is $200 ("system" model). Check 'em out At:

http://www.extremeshelter.com/products.htm