[smc]

Are you looking for a structure that is simply there to support the seats and harness? Or are you looking to build it to the specs of a race sanctioning body? Do you want it for the look, or functional? Di you plan on driving this car in the street? How tall are you?
There is a variety of designs you can choose from to meet you needs. The biggest problem of our cars is the lack of head room. You Best bet is to bend up a main hoop that goes just behind the B pillar, then ties into the rear strut towers. This will be a sufficient roll bar with the ability to keep the roof from crushing in, and mount your harness straps to. If you daily the car, avoid roof bars that run by the doors. If you ever crash, you likely to crack you head open on these with out a helmet on.