G.L.O.C.K. – LOCK them out if you can’t get out.
Barricade the doors and windows.
Do not all be together in one area. Spread out.
Everyone pickup something to throw at his eyes when he enters the room.
G.L.O.C.K. – Knock them out.
Everyone throw the objects at his eyes when he enters the room, then everyone pounce on the guy the moment he flinches.
Grab the man’s gun from the top with both of your hands and quickly twist it out of his hand by grabbing the gun tight and close and pivot your whole body as much as possible until the gun breaks free from his hands. Immediately after you pull the gun away, swing your body with elbow extended straight back at his head with full force. Repeat hits with elbows, knees, etc until you can shoot him dead with his gun.