Convertible Roll Cage, pls help me out...
 

I'm planning to build a roll cage for a vert. what is the most effective design as far as weight and safety? also what type of metal should i use and the gauge?

Take it to ISC and ask for an SCCA-legal roll cage. Their work is decent and they have pretty good pricing.
http://iscracing.net/

The chances of you making a correct roll cage on your own are close to zero, but you can see the SCCA GCR Appx. G if you insist on attempting this yourself. Unless your car is stripped, I would go with the 1.750 x 0.120 DOM tubing as a minimum.
http://www.scca.org/documents/Club%2...CR/2009GCR.pdf

Pics of an EP (mid-level competition) convertible:
http://www.mazdatrix.com/faq/epconv.htm

Do you have a welder, tubing bender, tubing notcher, and the skills and knowledge of how to use them properly?

Roll cages are a serious piece of safety equipment, and if you are not confident or proficient with the tools listed above you shouldn't attempt to build one yourself.

Sorry if I am coming across harsh but it doesn't seem like you have any knowledge of fabrication or have done any research about this....

What are your plans for the car? I share a shop with a guy that has an EProd vert. It has no windshield as allowed in the rules. I did a little work on the cage to bring it up to new rules. If you want to see pics of what it has PM me. If you want to bring the car to the St Pete area I can do one for you.

You can use 1.75"x.095 DOM on the car because SCCA goes by what weight the car has listed in the rules for what it requires for safety. But Evil is right, the vert chassis is a pig already and it will be tough to get it down to EP minimums if that is what you are shooting for. I can also help with fiberglass parts for the vert like a fglass trunk lid as well as full EP legal bodywork.

Do you actually make FG trunk lids? I may be interested in 1 if so. I've been looking for one forever. You could probably sell a ton.

Yep, its designed to be held on with dzus fasteners though. Its a foam core skin basically, it weighs maybe 2-3 lbs. I've never weighed one though but I know its not much. With some work it could be made to work with hinges and a latch. PM me.

thanks for all of the great info guys. I am not skilled or generally familiar with the tools and skills. but this is not a me project its a family thing. the people that will be working with me on this go from skilled professionals to novice (myself), so as im not going to be confident with all aspects, thats where the skilled hands and minds of others will come in.