ok you say 3 colors, like four corners are one color, the four middles are one color and center is a third color?
If so, you will make 12 blocks that measure 13" before you sub cut them to get a 12" finished D9P block!
for each fabric you need 1 yard and if you use the center patch fabric for a 3" border you will need to add 1/2 yard to that one.
You will be cutting 4 1/2" strips, and you can sew them into sets of color 1, color 2, color 1 as a set and then color 2, color 3(center) color 2 as a set, you will more sets of the first combo than the second of course.
the total size would be 45 x 58! with a single 3" border!
you can do 5" strips, but the blocks will be bigger!
I hope this helps!