Here is how I would do it. You can make HSTs or Half Square Triangles(Flying Geese) and then all you need to do is cut out squares for all the rest ecxept for the block at the top in the middle. That will be the same length as two blocks sewn together. I would strip piece that and then cut it to the size that matches two blocks sewn together,
My EQ shows the long strips as blocks but you can sew a strip on the sides instead of the tan blocks as this shows
Here is my tutorial on making HSTs and to make a 12 1/2" unfinished quilt block you will need a 2" template.
Or cut your squares and HSTs with a ruler so they are 2" square.
http://www.quiltingboard.com/t-37915-1.htm
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