Is 6 x 6 the finished size of the block? By finished I mean the size it will be when it is surrounded on all 4 sides by other fabric. IF so then the following measurements are correct. The solid squares (green) will also be finished at 6 x 6 --- the same size as your attic window blocks. So the cut size would be 6 1/2 x 6 1/2. The side setting triangles would be cut at 9 3/4 inches then cut a big X from corner to corner to make 4 triangular pieces. The number of 9 3/4 squares you cut depends on how many side setting triangular pieces you need -- how many rows there are.... The corner setting triangles --- make 2 squares that are 5 1/8 and cut them 1 time from corner to corner to make 4 corner pieces. I hope this helps --- if you need more information---please ask.
There is a great book put out by Better Homes and Gardens called "Complete Guide to Quilting" --- it is a great reference book --- I use it a lot.
Do you still need help with the narrow sashing that surrounds both the attic window and the solid blocks?