Thanks for the feedback and reccomendations.
I am thinking a 1.75-2.0" diameter, 0.120-0.125" thick bar (that is about typical right? My first roll bar).
I doubt I would have CAD for it. If design is a big issue, perhaps I would be ahead by buying one of these "family cages" and making small modifications to it as I like...? Just have someone weld it up?
(ebay item 330597413263)