It's super duper easy to make a skirt like this. I just chopped off the bottom of the dress and then cut up vertically to create a long piece of fabric. Then I took the fabric, wrapped it around my waist and pinned it where it fit, then cut off the excess. Then I folded and sewed a 1 inch hem at the top. I am using the original hem for the bottom of the skirt since it's even easier that way. Then you just thread some elastic (cut to the size of your waist plus maybe an inch and a half) through that hem you made, gather the elastic then sew the ends of the elastic together with the fabric. Done and done!
(don't mind the missing needle...I had just broken it before I decided to take this photo. hehe)