Buying fabric that way gives you pieces of an entire line. It would depend on what you want to make as to what you should buy. I've never purchased any of the precuts, I prefer buying yardage myself. I wouldn't worry about buying fabric in order to build a stash - I would look for a pattern (or design your own) then buy the fabric for that particular project. Your leftovers then go into your stash. It won't take long before your stash is breeding in a dark closet and you have more than you know what to do with!