I didn't really use a pattern for this, but I took an easy sort of evening bag shape, and made it really big to make it an overnight bag. It sort of went flopsy-doodle on me. (I should have used a fabric with more body, and maybe some interfacing.) You can't see it because my camera is less than thrilling and the bag is black, but it has a nice inverted pleat in the center of both the front and the back, and I squared the bottom.
Hanging up and looking floppy:
Flat on my embarrassingly unmade bed:
And a close up of the trim, which is the best part of this silly bag:
I will be able to use the bag, though. Being stuffed full of clothes helps it to retain its shape. Let's just call this a learning experience. (That's what my Dad always says, anyway...)