I had the choice to have it made from steel or aluminum. Since they have a lot of aluminum stocked at their shop that was the route they decided to take for me. My original design in CAD had it being milled from a solid peice of aluminum. They were able to make it out of Sheet Aluminum which definitly helped in the cost factor. It was a little labor intensive to roll the standing lip and weld it to the flat ring, but it turned out awesome.
Also by making it out of sheet aluminum it gave it the ability to form with the existing hardtop. In case you haven't looked at the top of your truck much, most are a little wavy and dented in places and when you cut the opening in it, it gets a little worse. The metal hard top is made of very, very thin metal and it is a b*tch to try to weld or patch if you have too.
I will try to take dimensions when I get home tonight.