Omi- I second the RRP suggestion- for a free pattern, it's pretty good

I haven't done the AIO version, but that's just because I prefer being able to "unstuff" a diaper for the wash. You could always make a fitted to start with as practice if you are a bit unsure- it tends to be the waterproof stuff that is costly but the general shape of a fitted is pretty much the same as an AIO (and fitteds tend to be more forgiving with fit too so you'll probably still have something quite useable even if it doesn't turn out quite as planned!).
Flubdub- for a wetbag, you could just use shower curtain material if you'd like. Our fabric store sells a waterproof nylon that I made our first wetbag with and it works great. One of the online diaper fabric stores that I use also sells pretty much the same stuff too. I probably wouldn't use one of the cheap dollar store shower curtains, but the nice waterproof nylon works well