I buy a piece of fabric when I like a piece of fabric and it goes into my stash. 1/3rd of the time I buy all the fabric for a quilt top project. But when it come to starting a project, I always start out with a plan or pattern. And almost always change the plan or pattern along the way. I may enlarge or decrease the size, don't want to finish the borders as shown, not have enough fabric to complete the borders, or blocks. I may change one of the blocks b/c I don't like the block, or the way the block goes together, or I figure out a better way. Most of the time I change one or all of the colors in the pattern. I guess I only use the pattern or plan as a starting point or guide. Very rarely do I practice making a test block. I usually think about a project for months or years, before I start working on the project. Then I sew and quilt and start the creative process.