i built a rack for my '80 toyota truck, 2"x3" steel for the main hoop right behind the cab and a mix of 1 1/2" square and angle for the rest. i bought the "sunbrella" canvas material to make a top for it but stalled out on the project. i had all kinds of grand plans for it, hard sides and top, maybe a pop-top of some type. i did make sides out of some angle that connect together to make a ramp for my snowmobile this winter (the rear crossbar of the rack is removable for sled/tall items). i'll try to find some pics of it and post.
i'd say build your own. all in, MIG welder and steel was still cheaper than a new fiberglass topper and you get to add all your own details.
clay