One of the things I wanted to do after buying the car was replace the rear window on the hardtop. It was cracking in a few places and overall wasn't in too good of shape. It was also not held on as well as I would have liked. Well during one of my sessions the first time I was out - it cracked really bad.
I looked online and found a couple places that made them but they said they couldn't guarantee fitment if it wasn't their hard top. So I had a friend who works for a sign company make me one out of 3/16th's lexan. He also put some black vinyl around the inside edges to trim it out. I did a tracing of the opening and sent it to him and he uploaded it to CAD and then had it CNC cut at his shop.
I fastened it with 5mm stainless button head screws with stainless washers and locknuts. Also used small rubber washers under the washers where they met the lexan. You will notice the extended aluminum pieces on top. The portion of the roof where the top of the lexan sits was very narrow and I didn't want to risk drilling it or the lexan for fear of cracking. The original window was held on by these aluminum pieces (you can see the black rubber plugs in the roof. So I used those to create the three top pieces. There are also small pieces under the lexan which then extend into the inside portion of the roof and act as a clamp to hold the window on. Quite happy with how it came out.