I wasn't sure how much I needed, just painted what I thought might work. None of the scrap pieces I had were long enough to go across the whole window so I knew I would have to cut them into sections.
The next thing I had to decide was how to attach the wood to the very narrow interior window strips. This problem led to the happy solution of running the wood in opposite directions. I used the nail gun to attach the pieces, had to shoot straight and did miss you a few, but only a few.
This really is a relatively simple project and so fun to see it come together!