If you are making a quilt that's 50 X 50, are you thinking it would be 5 blocks ( 10 inches each ) across and 5 blocks down? If so, I think you might want to go with a 10 1/2 inch block for the pattern you are using. Since the nine patch could then have 3 1/2 inch squares or to put it another way, you would cut them at 4 inches and they would finish at 3 1/2 inches. So, 3 /12 plus 3/1/2 plus 3 1/2 would equal 10 1/2.