Jack, I think it might be helpful for us to understand why you want to build one. Low cost? Or do you have the building bug?
I see that you're 13 and in another thread you were looking for help on how to throw a shuv, I do believe. That would lead me to believe that you're interested in a skim style board...I'm not sure the above references will be all that helpful...they are more surf focused.
Practically speaking, if you're 13 unless you are REALLY developed for your age, you're no doubt under 100 pounds. Have you thought of just buying one of the fiberglass skimmers off ebay, popping a fin in it and maybe some traction? I think you can get a suitably sized skimmer for around $45 shipped to your door. If your motivation is low cost, you'd have a hard time building one cheaper than that.
This is an example of one on eBay
Keep us posted 'bro.