I've sewn clothing for years. I used to watch my mother make her own clothing with no patterns and asked her to please teach me how to do that. She (in her infinite wisdom) said, "No, first you have to learn to do it with a pattern, then I'll teach you the short cuts." This is what I suggest for you too. Take the classes, learn to sew from other's patterns, learn to adjust those patterns to perfectly fit yourself, learn to adjust them to fit others and then you'll have learned what you need to know to make your own. Like that afore mentioned wise woman used to say,
"You can't put the roof on till you build the barn."
However, so that this post isn't a complete downer, take an outfit that fits and cut your own pattern from it without taking it apart. Then sew it together and make it fit you. When you can do that you'll be well on your way.
hint: it's all in the folding.