Sorry guys, I was pretty unclear in my first posting! I actually wasn't speaking about the roof material, just the basic shed! (I fixed up that first post.)
After searching for weeks, re-measuring the deck space, etc, etc, I've changed my mind about what I am going to do. Instead of a shed with a rool up roof I'm going to construct something smaller that rolls off the telescope. The nicest one I've yet seen is here:
http://mmerino.com/resources_astroph...l_off_shed.htm
I've seached for something prefab but so far no luck. (I need a shed about .75D x 1.2 W x 2H meters.)