I thought I would include the math & dimensions for Libby's Christmas quilt I made her. The blocks were pretty simple. They are 12 1/2" blocks- there were 25 total blocks for the quilt with 6" sashing on the outside. Finished quilt came out to about 72" X 72" square.
Back to the blocks...I had 6 colors of the flannel - I prewashed & dried all the flannel, actually did the Red twice. I was a little worried about the red, not sure if it would bleed or not. So I washed & dried it twice. I had 2 'sizes' of blocks. they were all 12.5" blocks, however the inside dimensions were a little different.
All the solid Black, White & Grey had 8" blocks on the inside- adding 1/4" on each side made it an 8.5" block. the sides with seam allowances came to: 2 cuts of 2.5" X 12.5" and 2 cuts of 2.5" X 8.5"
For the Black & White Damask, Red and Grey & Black print had 5.5" blocks on the inside (including seam allowances), the other cuts were 2 cuts of 4" X 5.5" and 2 cuts of 4" X 12.5"
No specific layout or pattern on how I arranged them, but I tried to have patterns & solid opposite each other if possible.