I think your crazy to want to do it too, especially since there are so many great armor kits already available. But if your main purpose is wanting to do it just to do it, then go ahead. If your main purpose in doing it is to become a stormtrooper, then I'd suggest getting a kit.
It you do decide to mould your own, I'd definitely purchase a kit to get a good reference on how others have done it. As long as you are getting it and not recasting it, you'll probably get much better results with your sculpts. Think of it as drawing a person out of your head vs. drawing a person with photo reference - big difference.