I normally buy the fabric when I find it and then try to find a pattern (or block) that will look good with it. When figuring how much fabric I need to buy, I assume 40" in my calculations. If I am buying for a pattern, I always add 1/4 to 1 yard extra to accound for shrinkage or if the calculations are based on a 42"-44" width. I like my borders to be LOF with no seams (unless they are pieced, or the fabric pattern requires WOF) and if the pattern maker figures on a 42-44" width I may not have enough for the blocks after I cut the borders.