I need fat legs
Although it is theoretically possible to do fat injections to make skinny legs fuller, this is fraught with problems. First, if your legs are thin, the rest of you probably is too. This means there is probably very little fat that can be harvested. Secondly, getting the fat to take everywhere and getting a smooth contour in exceptionally difficult. You are better with working out to enlarge the muscle and eating a little more to add a little fat generally (unless your legs are totally different from the rest of you).