Hi My name is Jerry Assburger (Fat Old Guy) and I have a Karting Problem.
Welcome, kidmakecart! If you roll your own design, here are a couple of Assburger's pointers....
Base your design off what's available or affordable, running gear-wise. Price out your wheels/tires/axles/spindles and get an idea of what you can run with. For a powerplant, be flexible. If you fabricate a mount for a B/S flatty, you can always mount literally dozens of other motors in the same place, should you want to try something different.
As STUPID as this sounds, find a floor that has 12"x12" linoleum tiles, sit down on it, and record on paper where things are. (Where your feet end, where your butt is, how wide, when you're "steering", where your hand placement is...) as dumb as this sounds (don't let people catch you doing this!) it's a great way to lay-out the basic placement of things. Get out a book of graph paper, and fill every page with details of where you're going. You'll end up throwing a few pages out, but that's evolving your design, and that's normal.
I built the 1st Lowrider using this design practice, and except for over estimating the effectiveness of the front brakes, it's been a 7/10th's success. I also thought that 10" off the ground was "low enough" to corner well, but not for a trike.
The Lowrider v.2.0 is also being designed using this process, and so far, so good....?
Good Luck, and welcome! Post your progress. We all have something to learn from each other.
hi im 12 turning 13 in a bit i like working with my hands an im thinking about makeing a go cart but im not really sure about blue prints and stuff plz list some web sites with free blue prints and tell me wat i need 
