If my math is correct, if you use 2 Jelly rolls it would be 100 in x 64 in. Not a great measurement. Rather than using a jelly roll, what if you found a few fabrics at 1&1/2 yards and cut 2.5 in strips lengthwise, so they are 54 in lengths, instead of the 40 - 42 in. Then if you use 40 strips your quilt would be 68 x 64, and if 708 use 50 strips it would end up 84 x64. It seems no matter what the length of the strip I was coming up with the 64. But if you went with a 3 inch wide strip you could go with 50 strips, 54 inch long at 3 in. wide = 84 in wide and 96 in. long.