I wanted to build a roll cage for several reasons . the primary reason being the fact that the seats sit outside the outer chassis rail, the cage would provide some side protection. Other reasons include providing a hard point to mount seat belts. Also stiffening the chassis for handling reasons. It will also incorporate door mounting plates and a steering column support.
To the left you can see the tubing I started with. 20 feet of 1.5 x .090 wall round tube and a 6 foot drop cut of 1.5 x .250 wall square tube to make the steering column support/knee bar.