After entering a long final approach for landing, the engine lost power. While attempting to restart the engine, the pilot noted that he had not previously turned on the carburetor heat. He was unable to start the engine and maneuvered the plane to land in a parking lot. Before touchdown, the plane struck the tops of trees as the pilot was avoiding powerlines by crossing below. He was unable to stop on the parking lot. The plane struck trees and a fence on the far side of the lot. An investigation revealed that the temperature and dew point at 2000 ft were about 32 degrees. Above and below that altitude, the temperature increased to about 42 to 45 degrees. During an operational check of the engine, it would not start until the carburetor was drained to check for water. About 1 1/2 oz of an unknown substance, heavier than fuel, was drained from the carburetor. The plane had been flown 5.3 hrs since the last refueling on 11/8/81. Nearly one quart of water was drained during the preflight.