I have made a couple pair of these. Some girls at my church wanted me to show them how. We got together one afternoon and made a couple pair. I forgot to take my camera that day though. We even made some out of men's polo shirts. They turned out pretty cute, but we needed a little bigger shirts. This is the pair that I made for my daughter. I made a waistband casing out of some fabric I had. I just put some wide elastic in the casing then. It took no time at all.
Here she is modeling my grocery bag I made as seen here:http://www.craftster.org/forum/index.php?topic=177482.0
here is another shot of the waistband. Sorry about the camera strap, but the camera died and this is the only shot I got.