Jim,
I had a well house made of concrete block. The mason put some anchor bolts in the top blocks in order to anchor down (flat) some treated 2x8s. Then I had a sheet metal man make a top out of galvanized sheet metal. It was a regular gable roof, roughly 2-12 pitch. It had a treated 2x4 screwed in the ridge and one on each side for stiffeners. The sides overlapped the treated 2x8 and was held on by stainless steel wood screws. To remove, one person could easily remove the wood screws, lift one end and slide it away from you, walk around to the other end and slide it on down off of the building. I had a light mounted on the wall on the inside and a weatherproof switch on the outside.