Hi, just wanted to mention that you might want to check out the Sewing and Crafts board...there are lots of home-diaper-sewing mamas on the board, and there are frequently posts about sewing diapers.
As for sizing, if you're going to make diapers for your own use, you can always use a pattern...I like the Honeyboy home pattern myself. Or trace a diaper you already have that fits your ds well! Of course this doesn't work if you're also thinking about making some to sell..
I have had good luck getting fabrics through co-ops, mostly in yahoo groups. Just do a search for "diaper fabric" and you'll turn up a lot. If you'd like more specific info, feel free to pm me.