EE AND COWORKER WERE IN 5 WEST TO 6 HAND SCALING ROOF. THEY WERE APPROXIMATELY 60' IN THE AIR NEAR THE ROOF. THEY HAD SOUNDED THE ROOF PREVIOUSLY AND IT SOUNDED SOLID. EE WAS REACHING TO SCALE A ROCK ABOUT 4' FROM BASKET WHEN THE ROCK ABOVE HIM FELL. FOUR ROCKS FELL, SOME STRIKING HIM, RANGING FROM 100 TO 500 LBS. COWORKER WAS NOT HIT BY ANY ROCK.