See if this works..get a piece of string and tie it around a waist ( thats what you are trying to make right ) tie it in a bow and leave the tails the length you desire. You will now know how long you want it , then you have to decide the width. Buy your fabric. Go by your width and double fold on the fold......the end taper so they form a point like a ribbon or cut in V shape if you want that look. SHouldn't be too hard to do Good luck