http://fernandfaerie.com/sewing_fitteds.html After trying a few different patterns, this is where I found the pattern for the style of diapers we liked the best.
I used the pattern that is on the above link, but made a few changes regarding materials used, and a few changes to the method of making them.
Since I was using a serger, and the serger would could the material for me as i sewed, I did not cut out the pattern precisely. A pattern was cut out of an old pizza box. I then transferred the pattern onto the liner material using an ink pen. (The line would be cut away by the serger) For the inside of the diaper, i used cotton flannel -one yard made approx 10 diaper liners.
The material here is folded, so once I had all the patterns "drawn" on the right side of the material, I cut them apart and would then turn the material over and then mark the pattern on the other piece of fabric. (by cutting the material while it was folded, it saved cutting each liner individually)
For the "soaker" part of the diaper, I used a washcloth. (purchased in a multi-pack at wal-mart - they look thin at the store, but once washed and dried, they really fluff up) You can tri-fold the washcloth and serge the edges, or just tri-fold and go!
You're now ready to sew it to the diaper liner. Place the soaker under the liner and center it between the sides and position it where you want it front to back. Flip it over and pin in place.
Now sew around all the edges of the soaker.
Now it's time to sew the liner to the outside of the diaper. For the outside of the diaper, I use 2 layers of t-shirt material. Pin the liner to the t-shirt material and serge the side edges only - leaving the top and bottom open. It is not necessary to mark the outer layer with the pattern, I just lay the pattern on the material and cut it out a large square...the pattern is already marked on the liner and that's all we need.
With the sides serged, we're ready to sew in the elastic for the leg openings. (this is marked on the original pattern) You might want to experiment with the length of elastic to use. The first batch of diapers i used 5-1/2". It worked fine, but made the diapers seem a little smaller, so I used 6" and the diaper fit much better.
Place a mark approx 1/2" from end and again at the length you want. Do not cut the elastic until it's sewn in the diaper.
When you reach the mark on the liner material, pull the elastic until you see the mark you made indicating the length. Back the elastic up so that the mark on the elastic now matches up with the mark on the liner. Raise the pressure foot, turn and stitch across the elastic to secure in place. Cut the elastic now approx 1/2" from where it is stitched.
Repeat stitching the elastic in the next leg, cut the elastic and you're ready to serge the top and the bottom of the diaper closed. That's it!