Started with cardboard, then 1/4” plywood, then a scrap piece of plexiglass for a pattern. That took time, patience and a couple of nights to get good.
Once I had a pattern firmed up I have access to ACAD and made a drawing, sent that to my buddy who has a small plasma CNC and he burned it out for me in a piece of scrap .020” aluminum I had.
Then took to an auto glass shop and they cut and installed a piece of auto safety glass and gasket.
I have $200 into the windshield between the plasma cut and glass shop and also made my own aluminum roof out of aluminum to tie into windshield.
My advice - you can purchase scratch resistant lexan on both sides from eBay and just cut and get on with it or go down the road I did. Even without a plasma CNC I am confident I coulda cut with straight edges and a jigsaw.
I still need to perfect the gasket but for now used foam pipe insulation.