I posted the Snapazoo template on my diaper-sewing blog a long time ago (when Kamsnaps.com was posting about them).
I actually owned a retail Snapazoo a LONG time ago. I'm not exactly sure how they made such a nice turned edge on theirs, however, I found that using 3 layers of a fairly thick fleece and just sewing close to the edges works quite well (fleece being no-fray and all). Also, long-prong snaps are your friends. ;) You can make them a little thinner if you don't have long prong snaps, however, they won't be quite as rigid when all snapped into shape.