Yea, it is just a metal sheet.... as is the rest of the car... hehe.
But what you'd want to do, if you were wanting to recreate the entire skin, and have it be only CF, would be to carefully remove the roof, leaving in place the metal girders that support everything. Then, the CF roof would be 'panelbonded' (neat product, and STRONG) to the metal and the girders.
It CAN be done, but to do it, would require making a mold of a stock metal roof, and then pulling a part from the mold. Again, not impossible, but cost prohibitive... and what is the benefit? Much like CF fenders, the metal counterparts aren't that heavy. So if you want the CF -look-, then you have someone experienced with CF overlay the stock metal pice. Ya, you're adding weight i suppose, but it'll be 20x less expensive to accomplish, and it won't require major automotive surgery
Keep in mind also, to remove the roof completely requires that you remove the windshield... and 50/50 shot, but most crack upon removal, which means a new windshield as well.