he is using the scorpion go kart plans by spider karts, which calls for 14ga, 1" sq tubing. i remembered a few things to look out for other than the steering.
1. i wouldn't suggest getting the spec seat, i bought it but feel like i got robbed because of what it cost me.
2. make sure you can weld 1/4" steel, or have someone that can.
3. try to make your own shock mounts, bearing mounts, etc, save some money.
4. use big Heims for the rear swing arm pivots, not the spindle brackets in the plans.
5. save as much money on parts as possible!