If you plan on building a roll bar, hoop, cage, or any form of ROPS that you actually want to trust your neck to, you're going to need a lot more than a couple suggestions and/or pics. I don't want to play the heavy here, but this is NOT something that you just toss together out of EMT and JB Weld.
I was about to type out a list of Do's and Don'ts. Then I decided that if I HAVE TO, you probably shouldn't.
Could you maybe illustrate your plan/purpose in more detail?