Not meant to discourage you but 120x120 (10x10 12" blocks) is pretty darn huge. I usually use the old guide of 3 yards square or 108x108 for king sized, but that might not give you the drape on the sides you want. How will you hold the quilt together? Most long arm quilters only have frames that are 10 or 12 feet long. You can tie the quilt or even force it through a sturdy sewing machine with a reasonably large throat but it will be a handful!
3 rounds each side plus a center can also be hard to pull off in a 12" block. This link shows you a 12" (finished) block and gives directions with 3 colors each light and dark but no separate center.
https://www.bobbininquilts.com/blogs...hnique-tuesday
It uses the 2.5" cuts I was mentioning in my first post, so you will get (16) 2.5 cuts per strip with the other measurement being how deep each strip is.. With 100 blocks, that means you need 6.25 strips per each size and color. so you would cut 7 strips plus have some left over. I am a believer in prewashing and have often been burned with bad cuts so I usually get more than I need, even with most of a strip available for extras. The yardage in Parentheses is what I would buy and is sometimes very close tolerances.
A (light center square/round 1) = 7 strips X 2.5 = 17.5 inches (2/3rd yard)
D+E (light round 2) = 31.5+45.5 = 77 inches (2.25 yard)
H+I (light round 3) = 59.5+73.5 = 133 inches (3.75 yard)
B+C (dark round 1) = 17.5+31.5 = 49 inches (1.5 Yard)
F+G (dark round 2) = 45.5+59.5= 105 inches (3 yards)
J+K (dark round 3) = 73.5+87.5 = 161 inches (4,5 yards)