The boy, 14, was cited for trespassing at Trabuco Hills High School in Mission Viejo, The Orange County Register reported.
Orange County Sheriff's Deputy Darren Sandberg said that the 14-year-old and three companions managed to climb to the gym roof via a lifeguard tower and two other buildings on Sunday afternoon.
"It's a popular place to skateboard," Sandberg said.
The boy, in spite of having broken a wrist, his pelvis and some ribs, managed to get to the door of the gym and to get help from his friends. He was transported to a local hospital.