My Custom D&D wolrd has a very specific magic system which is tied in with politics and history and other asspects of the world. Is it better to start a Magic system from Scratch or tweek the exisiting 3ed rules to fit? Keeping in mind that I am bad at math and that my previous (non) system left great room to be abused though my faithful players of three years seldom did so and intimadated the heck out of any new players who tried to, I am leaning towards tweeking the existing 3ed Sorcerors rules. Any Suggestions?