Making or maniuplating clothing patterns?

I'm trying to learn hot to manipulate or change, or even make new paper patterns for making clothing. But, I am having trouble tracking down a web site/book/ or whatever might help teach me how to. I'm very good at making clothes from already made patterns, and I knit and crochet very well but really would like to learn how to make my own clothing designs but from my own patterns. Could someone tell me of a site/book/ etc. that teaches how to manipulate or teach how to make my own patterns. thanks.