I went through the whole cage thing a little over a year ago. Chromo Vs. DOM , sizing, and sanctioning body tech requirements. Here's a couple links to threads you might find informative. Beware of assuming that rollbars and cage structures you see in PT type cars are legal for any sanctioning bodies. Get the rulebooks for any sanctioning bodies where you might run the car.
https://lateral-g.net/forums/show...light=chromoly
http://www.pro-touring.com/forum/showthread.php?t=48151