Hi, I want to make a carbon fibre or carbon kevlar roof for my car. Just want to know which material suits better and how many layers should I use in the resin infusion.

For a non caged car (and even for a caged car really), I would recommend at least one layer of kevlar or carbon/kevlar somewhere in the layup.  main reason being to keep the roof in one piece (albeit cracked and bashed in) in a roll over based crash, and also to prevent lots of carbon splinters coming into the cabin.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant