After you cut the pair of boards, put them atop each other again and make sure they are perfectly sized. If one board is even 1/8" off - it will make a difference later ... so be very patient and very picky!
Once one pair is finished, do the exact same thing for the other side of the frame. Repeat blogs 6 - 9. After this, you should have the frame cut. In our case, we have 2 6' boards and 2 4' boards with angles on all ends.