This is a really great tutorial if you follow the link :) I loved how easy they were to make.
The original version has you piece together 4 different fabrics to make the top fabric. I did this on a few of mine, but did a few with just two large bits of fabric instead. It also called for interfacing, but I ran out and didn't feel like going to the store. They seem to work just fine with out it, but it would help to keep its shape a bit better. And lastly the original used a snap button, which I don't have access to so I just used regular buttons and sewed a button hole on the top flap.