If you plan on welding your own cage, you need a halfway decent welder first. The baby welders sold by home depot will NOT cut it. They'll lay what looks like a weld, but they can't put out the power to weld .120" wall tube. A good 110V machine can do it, but a 220V machine is better.
And make sure you take the time to practice enough before hand. It's easy to lay cold welds with MIG that look ok, but are weak. Remember that your drivers are trusting their well being to your welds. Take the time to practice, then practice more, all on bits of roll bar tubing. You'll need to know how to lay a good weld when you can barely see what you're aiming at. Welding in a cage is nothing like welding at a bench.
I'm not saying you shouldn't learn and try it, I'm just urging the necessary precautions. It took me a couple years of welding before I felt confident enough in my ability to weld a cage I trusted my Dad to climb into.
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