I don't like this one, it's kinda ugly, but I like the idea. DIY Sweater (mini) skirt - can be as short or as long as you want, depending on the size of the sweater you use to start. Definitely want it snug though I think, so take in the sides if need be.
If you have long arms (like me) and a bunch of long-sleeved tees that don't fit after one wash and dry, you're gonna love this idea. DIY – Long sleeves to short. adding long sleeves to a short-sleeved shirt HAHAHA