The pattern says it makes a quilt 68" x 95" (5 blocks by 7 blocks or 35 total blocks). You'll want something not quite twice as wide, and a little longer than this one, maybe shooting for 108x108", which is evenly divisible by 13.5" -- 8 blocks each side (64 total blocks), or so 7 blocks each direction plus borders (49 blocks).
To make 8 blocks x 8 blocks multiply the yardage by 64/35 (1.8) and round up, so maybe 2x the yardage.
I like the color scheme in the tutorial.