Begin by making a rough layout of your window grid on the pillow using rectangles of scrap paper. You can let your little architect figure out how big he wants his windows to be; the green pillow shown here (from Pier1.com) fit thirty windows that were 2½ inches tall by 1½ inches wide.
Once you have a design you’re happy with, cut rectangles from black and yellow felt. Cut one yellow rectangle for approximately every five black.
Lay out your window pattern on the pillow, interspersing yellow windows as you go. Glue the felt windows to the pillow, making sure you apply the glue to the outermost edges of each rectangle. Let dry for at least an hour before reclining.