i built my frame from 20 feet, but used some angle iron for the steering support, so id buy 40, because you may mess up a few prices, my go kart i built i used 1x1 10 gauge (1/8") and it is not too heavy, princess auto sells 13-5-6 tires for 30 bucks, but you can get them on sale for 10 bucks, there a decent size, and you can find replacement tires real easy, id recommend a live rear axle, winter is coming!, and trust me 1 wheel drive is **** in the snow, you can also buy 145/70-6 knobby tires from princess auto and they fit the rims and give a ton of extra traction, you can get about 6 inches of ground clearence minus the brake a sprocket, they will sit a little low, if you want to use the 13-5-6 tires tell me and i will show how to lock them to an axle, my go kart was a real good size, a 5 foot person could ride it or a 6 foot tall person could ride it no problem, im about 5,10 or 5,11, fits me well, i can mesure it up if you want to build one kinda like mine,