I don't mean to doubt your abilities, but I would hold off on building my roll cage untill I knew exactly what I was doing and had all the variables worked out (wire size, speed, voltage). If I've learned anything from this board, it's that safety comes first. Again, not trying to burn anyone here.
"I am going to be using .35 wire but, what grade wire should I use on my 4130 chromoly 120 wall roll cage?"
0.35 would be some bigass wire! I think you meant .035, but as previoulsy stated if you dont have enough experience to select a wire type and size...I would stay away from chromoly and roll cages all together for safety reasons. Good luck in your project but I would build everything but the cage first so you can get more experiience and then go for the cage.
<A target="_blank" HREF=http://www.barneysprecision.com/fabproducts.htm> Fab Parts</A>
sorry i did mean .035 wire. and i am making sure that there is not some way or wire type out there to make my welds even stronger than they are now. i wanted to know if someone new more than i did. thanks for your concern though.