Nancy Zieman had a guest on her show that did them. I think her name was Mary Mulari (thanks quilterchick, I couldn't remember her name). Ms. Mulari has two books that show how to make them. I have both books, but have not done anything with sweatshirts. If I were going to do one, I would fold over the neck after I removed the ribbing, sew it down, make at hem at the bottom where I removed the ribbing, then I would make a button placket on each side of the front where you cut it. I would probably add button holes and buttons to the plackets, maybe add a pocket or two with the fabric used for the button placket and also add some embellishment, like applique or ribbon to dress it up a little.