Blueprints

This song is in the episode "Phineas and Ferb Interrupted" by Baljeet, Buford, Candace and Isabella so Phineas and Ferb can get their personality back. It was seen in the promo.

Lyrics
...

Baljeet: With these blueprints we can build this mighty tower

Isabella:With these blueprints we can make a giant chocolate ball!

Buford: With these blueprints we can fordge enormous yo-yos,

Baljeet, Buford, Candace, Isabella: With these prints we can build anything at all!

...

Doofenshmirtz: We got blueprints, glorious blueprints!

...

Background information

 * This was seen in the promo for "Phineas and Ferb Interrupted".
 * This is one of the very few songs that have the characters from both plots singing the same song, the other being "Busted".
 * First time in season 3 that Isabella has a solo line.