How thick are they? If they're the size of the things on the side of your house, that's incredibly thin, would potentially flap around like a limp dick without reinforcement, and would dent like supa said.
They would have to be really , really cheap to offset the extra cost of reinforcing them . Otherwise it's just as cheap to make them out of PVC //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif