According to the pilot, when he attempted to start the airplane, "the battery was low." He exited the airplane, instructed the passenger to remain in the airplane and how to turn the magnetos on and off, and he utilized the tail tie down hook and secured the tail down with a rope on the ramp. The pilot hand-propped the engine, it started, the throttle was "too far in," and the airplane accelerated forward. The "old" tie down rope broke, the airplane continued forward, and the passenger in the airplane turned the magnetos to the "OFF" position. However, the airplane impacted a hangar and then came to rest. The airplane sustained substantial damage to the firewall and right wing during the accident sequence. The pilot reported no preimpact mechanical malfunctions or failures with the airplane, other than the low battery, that would have precluded normal operation.