Advice needed on roll cage material.

[Peter VanDerWal]

I have a rather ambitious project to build a (mostly) ground up EV with a fiberglass body. Since fiberglass doesn't offer much crash protection, I want to integrate a roll cage into the foam/fiberglass body.

What I want is adequate protection should the vehicle flip at 65-70 mph.

Can anybody recomend a minimum tubing size, or a good book (or website) to read on roll cage design?