This is on my AE92 Trueno, and the reason is because the roof line is too low inside, due to the rails below the roof line and my helmet touches it. Plus the weight savings wouldn't go a miss

Has anyone ever done this?
What would be the best option for the material?
- Thin Steel
- Alloy
- Carbon Fibre
- Fibreglass
How to attach it to the roof?
- spot welds
- glue (anything suitable?)
- rivets
- body filler?
I already have a non-sunroof roof lining and even a cut out of the front section of an old parts car (ae92 levin). But it is very thick steel and would probably warp the roof with the amount of work needed to weld it flush with the existing roof.
Any help would be much appreciated.