The roof access door (on 2nd floor) is locked. Maybe someone in the staff has a key.
Try to find someone, or something, belonging to the staff of the mall. ?
You have to check the door and McQueen says someone should have the key.
Go ask the mallbot 5000.
You should ring dispatch to get your badges in order.
For some reason you, sitll, cannot access the squad car... But there ought to be telephone somewhere else.
Go talk to the mallbot and it will give you the key. You can now access the roof. Just use the key on the door.