Tony Scott asked for more money to film the rooftop scene in "Berlin" (in order to rent a helicopter for an aerial scene) but the producers refused. Scott believed that the scene was important and rented the helicopter with his own money.
Robert Redford was baffled by Tony Scott's use of helicopters to shoot the intimate conversation on the roof. But when he saw it, he was impressed by how dynamic it made the scene.
The scene where Robert Redford's character asks Brad Pitt's character if he knew anybody in 'this apartment house' and tells him to be up on one of the balconies in five minutes is from a book by former Mossad agent Victor Ostrovsky who describes this test as part of the training of a Mossad agent.
The pack of cigarettes Muir (Robert Redford) uses as a distraction are "Morley" brand, the same fictional brand used in The X-Files (1993) by the infamous character known as the "Cigarette smoking man".