The twin turboprop sustained substantial damage when it impacted the side of a terminal building while parking on the airport terminals ramp. After a normal landing, the pilot was maneuvering on the parking ramp. After stopping, the pilot put the throttles into the Beta range and backed the airplane about four to six feet so that it would align with another airplane parked on the ramp. The pilot reported then setting the parking brake and positioning the throttles back to flight idle before placing the propeller levers in the feather position. As he was putting the propellers into feather, the airplane taxied forward. He put the propeller levers full forward and put the throttles back into Beta. The pilot reported that the airplane struck the plate glass-sided building at about 3-4 mph.
