I did a windshield for an ultralight airplane I built. After I made a pattern I cut the polycarbonate with a fine-tooth jigsaw blade and sanded the edges to knock off roughness that might lead to cracks. Drilling mounting holes, I used a regular drill bit but ran the drill backward so the bit was more like melting through the material rather than cutting, which can cause stress and cracking. It's been a few years ago but that's what I recall of what I did.
Lynn