Dan Povenmire and Jeff Marsh describe how they created Phineas and Ferb and how they sold it to the Disney Channel. Instead of selling them a script, they pitched a storyboard, which is a scene-by-scene visual breakdown of how the episode would look. When it came time to present it to the executives overseas, Dan edited the storyboards together into a film, adding music, sound effects and providing the voices for all the characters. Jeff notes that after seeing it, Disney realized that they didn't want Dan to be the voice of Isabella.
The show is inspired by Dan's summers growing up where his mom would encourage him and his siblings "to do something creative instead of sitting around bored." His mom would say, "Summer's short. You gotta make every day count."
In the original rollercoaster, Phineas is shown having a hot dog, so that means that the idea of bending off a tree and ordering from a restaurant in the middle of the woods was kept.