Although I just did a sewn through differential baffle. Each baffle was 6.5" on the bottom layer of fabric and 11" of fabric for the top layer. This gives the "puffy" look and allows you to pull it tight against your butt without compressing the down.
Honestly it's very simple, 6 channels sewn and the edges rolled to allow the shockcord to go through, there isn't really much else to it Just measure twice cut once and be methodical.
Any more questions just ask, I'll be happy to help (although there are people here with far more gear under their belt)