My advice is "Don't worry about building a stash." You are better off buying extra for each project you do. I have a stash and I rarely have enough fabric in the stash for the pattern I want to do. If I bought 3 pieces of a collection - the pattern invariably needs 4-6. If you are lucky enough to find a great deal then buy but at today's prices I really think you are better off just getting a bit more than you need per project.