This papercraft is The Destruct-Inator Ray, one of Dr. Doofenshmirtz's inventions first shown in the episode, Ready for the Bettys of the American animated comedy-musical television series Phineas and Ferb, the paper model was created by joshua1533.
When Agent P snuck into Dr. D's new cave lair, he spotted this machine pointing outside the cave towards a bridge. He went over and looked at the Inator, but then Doofenshmirtz arrived, carrying his lunch on a tray. Agent P then leaped onto Doof's tray, grabs his long pointy nose, and tossed him to the ground. Soon Doof pulls out a tennis ball server next to his new invention and tries go stop him with it. But Agent P hits the server, causing it to spin. When it stops, the last ball hits the machine. The Inator's automated voice switches on and says, "Destruct-Inator Ray countdown initiated. 30 seconds until activation."
Then, as the countdown starts, Phineas and Ferb arrive in Perry's hoverboard. Agent P then pushes himself and Doofenshmirtz in a closet. Phineas marvels at the Destruct-Inator Ray, thinking that Ferb built it, but soon the countdown reaches zero, and a laser beam shoots out, destroying the bridge that the Bettys, along with Candace and her best friend Stacy were about to cross. Phineas then thought their mission was to save Candace, so they left. Then Agent P climbed out of the closet and pushed the Destruct-Inator Ray off of a cliff at the end of the cave, likely destroying it. [Source: wikia]
You can download this papercraft model template here: Phineas and Ferb - The Destruct-Inator Ray Free Papercraft Download