Titanium would be pretty expensive.
The cage should be put in the chassis while it's on a frame jig. Optimal safety, handling, structural rigidity and reduction of any stress in the chassis when adding a roll cage is done by jigging the car. It's the only correct way to really modify a chassis. It's almost like the tare button on a scale in a way.
For a street car, you probably should stick with a 4pt. and don't have anything coming up in front of your seats.
Make sure you prep the cage and paint it or something as well. Rusty cages in cars are so ugly, and eventually unsafe.
Plus, if you are getting to that level with your car, buy a fuel cut off switch, a real, certified one, and put it in. You might as well have that, and like, a mini cage-mountable fire extinguisher.
Your putting a cage in the car considering your safety ( cough*and performance*cough ), so you might as well have those other couple of things that can save your life or a lot of money.
The plates for your main hoop need to be welded on under the car. That means the rhino lining or any coating down there needs to be scraped, and holes cut in your floor board. Doing this assists in measuring the correct closeness of your hoop to the ceiling ( I think you want about a 1\4 of an inch ) by letting the hoop come up and down when it's legs have the floor to poke through. Ya get it in place, trim the legs of the hoop, weld up the plates on both sides.. yadda yadda.
Have a crossbar in the hoop, no shit.
I've heard of people welding up some rear suspension\chassis stiffening shit. Look it up here and Honda-Tech, you might as well while you're at it!
If you're also into more custom stuff like that while you're welding anyway. Consider fabbing up replacement bumpers for your car (the real ones, not the plastic covers). The generally rust out and provide very little real assistance in wrecks (we drive 20-16 yr old cars man). Lemme see if I can find an example picture of one.. it's on Larry Widmer's personal FOURTH GEN BABY:
