The fictional Nakatomi Plaza is the headquarters of 20th Century Studios, so the studio could use one of its own buildings and didn't have to hold back on stunts and action sequences. While Jeb Stuart was writing the screenplay, he did a tour of the building, and immediately incorporated some of the locations and objects he found there into his script as set pieces (such as the cart that McClane and Karl end up riding during their fight). The company charged itself rent for the use of the then-unfinished building. Some of the middle floors were occupied by legal and administrative departments, so only empty floors were used for filming. Still, the filming of scenes that involved gunfire had to be postponed until after hours because some of the employees from the active floors started to complain about the noise.
In an article for the 30th anniversary of the film, Bonnie Bedelia stated that the first thing she thinks of when someone mentions the movie is Alan Rickman. The two became friends and had lunch together every day while shooting the movie. She expressed how lovely and gentle Rickman was in real life.
The costume department had 17 undershirts in various stages of degradation on hand for Bruce Willis.
The scene where Bruce Willis and Alan Rickman meet up was unrehearsed to create a greater feeling of spontaneity between the two actors.
Alan Rickman nearly passed up the role of Hans Gruber, which ended up being his first film role. He had only arrived in Hollywood two days earlier and was appalled by the idea of his first role being the villain in an action film. To a degree, Rickman was right to be concerned considering his performance as Hans Gruber was so hailed that the actor had to struggle being typecast as a player of villains for much of his career.