my brother watches phineas and ferb so sometimes i watch it with him. its about these 2 boys who build giant contraptions that their sister trys to bust them for building it while their pet platypus, perry, fights the evil dr. doofenshmirtz [try sounding that out]. so you could kind of see how it would be a cool theme.
here is a list of possible sets:
there could be a set based off of the giant robot dog they build
or a set with agent p's lair
another could be based off of dr. doofenshmirtz's building