Go here and digest:
http://scolton.blogspot.com/p/motor-controllers.htmlLots of good info on all sorts of motor controllers. As a beginner you have no chance of making your own and making it work (realistically) far better to either make the one you have work or to buy one that does!
Motor controllers are the classic case where people who don't understand the complexities and subtleties inherent in high power electronics say "i'm not buying that $300 motor controller when a few mosfets are just $20, so i'm going to make my own" usually, several thousands of dollars later they are no closer to making a working controller.......
(Hint the reason a decent motor controller costs money is nothing to do with the part it has inside it, and everything to do with the amount of time and effort that went it to making it work robustly and reliably.......
)