Hi Angela.
There is a product called GRP (glassfibre reinforced Plastic.)
There are many roofers out there that can do this for you, but find one that only does thistype of roof. This should help to weed out the cowboys.
This product come in many colours and lead gray is the most common, this product will last 25 years and more with minimal maintenance, is not affected by standing water either, all this is subject the GRP being fitted properly.
Hope this helps
Joe Dybowski
www.simplybuildbetter.co.uk
Joe Dybowski, March 2011