Basically all you do is trace around your cell phone on some scrapbook paper. Cut it out. And then cut out a hole for the camera and flash ... I laid the clear case on the cut out cell phone shape and traced around the hole ... Once I got a good pattern cut out, I used it as a template for the other covers.
The options are as vast as your local craft store's paper aisle, and you could even create cases from your own drawings, photographs or collectibles (like a ticket stub or card).
You can find a clear case for your phone anywhere on Amazon.com, some are less than a few dollars. And of course, you can always leave the cover alone for an au natural look, if the mood strikes.