p>If you mean feeding rainwater into your natural pool from roof runoff, I would see no problem doing that with a metal roof, but shingles, particlularly older ones, may deposit toxic debris in it. This page would be  great place for you to start reading -</p> <p><a href="/guides/2237/natural-ponds-and-natural-swimming-pools/" target="_blank">How to Build a Natural Swimming Pool</a> </p> <p> </p