After completing an uneventful preflight inspection the pilot attempted to start the engines, however, neither would rotate. The pilot assumed that the battery was low, and that a low outside temperature had increased friction with the engine. He exited the airplane with the intention of rotating the propellers by hand, to increase lubrication within the engine. He pulled the left propeller through two rotations, and on the third, the engine inadvertently started. The airplane subsequently swiveled to the right and struck a building, causing substantial damage to the left wing. Examination of the left engine by the NTSB investigator-in-charge, revealed that with the magneto switch set to the off position, rotation of the propeller by hand did not result in sparks at each spark plug electrode. The pilot stated that the accident could have been prevented if he had set the parking brakes and chocked the wheels, as well as confirmed that the magneto switches were off, and that the throttle and mixture controls were set to retarded and idle-cutoff position.