Not enough information. You can't figure out how much is enough unless you know how big you want the quilt to be. If a jelly roll is 40 strips of 2.5"x40" fabric, then it can make at most a quilt that is about 56" square, but it will be less if there are more seams. For a log cabin you also need to know whether it's an even mixture of lights and darks. Also how many logs do you want on the blocks?