There are also rules on where the loop behind your head goes and it's relationship to where the driver's seat is at etc. A chassis guy will know all the fitment rules and get it right the first time.
Self-taught types just starting out can make a weld that looks ok with a little practice, but do they really know if the weld is strong enough? Look at the guys who narrow their own rear ends at home for the first time and the spring perches break loose on the starting line.
I will add, your helmet cannot be w/in 2 inches of any bar. Before you or anybody welds a cage in, get in the car with your helmet on and see where your head is. It would suck to get it all welded up and your head be too close to the bars...
