Here are my favorite (FREE!) directions on sewing pocket diapers.
Rita's Rump Pocket diaper pattern
I took some photos as I was making one of these and posted them in my favorite diaper message board.
Sewing a Rita's Rump Pocket diaper -- photo tutorial
Her directions are very easy but sometimes it is good to have photos you can look at.
The pattern calls for two layers of cotton so I used some old flannel shirts and other cotton fabrics to make our pocket diapers. It doesn't have closures like snaps or velcro on it so you can pin them to get a good fit every time. Some people like to use different fabrics for them and add closures. You can basically make this diaper any way you want; I found that I love it according to the pattern.