"Keep on Building", also referred to as "Floor After Floor" and "Tower to Nothing", is a song from the episode "The Doof Side of the Moon" to which Phineas, Ferb, Irving, and Isabella erect the tallest man-made structure in Danville along with the rest of the world. The method of construction seen during the montage is characterized by its sense of whimsy along with its defiance to reality and is possibly the most elaborate display of the boys in the act of building on the show to date.