I find that sometimes if I have a pattern first I tend to buy more fabric than I need. I keep finding fabrics that will work and before I know it I have spent way more money than I needed to. I guess I like to have choices, but then I tell myself that I'm just building stash. Isn't that the way it works? I'm hoping that once I have a decent size stash, I'll be able to shop from my stash and buy only what I need. I also buy fabric that I just love with no pattern in mind and will then buy coordinating fabric. Of course I have only been quilting for a few years and have been bitten by the fabric buying bug! But to answer your question, I do it both ways.