From the pictures you posted before, I would say the diamonds are 4 1/2" by 3". So.........if the pattern on the fabric is say 7" by 5 1/2" you have to cut the zig zag pattern those dimensions plus 1/2" seam allowance on both sides of the cut.
Look at the pictures. If the layout on the leather is 7" tall by 5 1/2" wide, the black dots on the cardboard represent those dimensions and are where the buttons go. The left side is how the fabric needs to be cut on the left half of the leather being sewed together. The right side is how the right half of the leather needs to be cut so that when they are sewed together, the two pieces interlock. When the final piece is tufted, the stitch lines will be hidden under the folds of the tufts.
There is another way to do it that involves sewing all the tufts in place and leaving small pockets where the buttons go.
No one lives forever, the trick is creating something that will.