You can frame the whole panel with an attic window, but it is probably more effective to cut up the panel. Remember, windows are rarely square. So, for example, if the usable part of the panel is 24x40, you might want to make the ACTUAL size of the individual window panes 8x10. 36x40 could be 9x10 panes. Whatever the size of the panel, you will need to devide it evenly in each direction. If you are not sure how it will be cut up, begin by laying strips of fabric across the panel in each direction to simulate the cuts.