I like the roof to be a solid one, so they can keep dry in the rain and shaded if its hot.
Our Guinea Pigs have one made from corrugated pvc sheeting, it is on a frame and sits over the ususal wire lid of the run, it slopes to let the rain run off but lets the light in. They are in a spot that doesn't get too hot for them in the summer but I can lift it off, just leaving the wire lid, if its sunny and they fancy sunbathing!
I'm with you jrn1310 in planning a walk-in run - I'm too old and round for all that bending at mucking out time and the other mum's at school must wonder why my jeans are always muddy on the knees!:lol: