Question about sewing those sack-like purse things

[girlx512.livejournal.com]

If I wanted a purse to look like the first crappy drawing (the seam being the dotted line) would I just need two peices shaped like the second drawing? I mean, I know how to make it lined and all that, but I just wanted to know if that's the correct shape to cut out, or if parts shold be longer, higher, slope less, slope more...



I love Ikea fabric and I was planning to buy some and make one of those purse things with it, but I'm just not too great at sewing without a pattern.