Piper didn't stop on the second floor, and he didn't turn around to see if Aaron was still following him. The closer he got to the roof, the faster he moved, and by the time he reached the door at the foot of the stairs, he was practically running. He lost his footing on the steps to the roof more than once, and by the time he reached the top he was just as out of breath as he was pale and panicked.
He didn't even knock on the sliding glass door to Daniel's apartment, he just slid against it and banged his head back against it over and over, again and again.