I found one of these on craigslist and the idea of making it a spray booth crept into my mind:
http://www.rubbermaidproducts.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=RHP+3673&Category_Code=Outdoor+Storage+Sheds
It is a little large, they make a smaller one, but the $487 price tag is steep. If I could get it for a couple hundred that might not be a bad deal, eh?