This is incredibly fun and fairly easy to do. I actually suggest that everyone try this once on a saved game.

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You need to get a key to access the generator room in order to open the containment doors holding back all the ghouls. There are 2 keys that you can get. If you ask around, you'll find out that Chief Gustavo naturally has one. You can do standard pickpocketing to get it off of him. You can also just go up to the suites to talk to Herbert Dashwood. This old
hero naturally wanted to explore the building, so he swiped a key for the generator room. If you ask about it, he'll mention it being in his inventory. You can pickpocket it, or just tell him that you don't have time for games.
With the key in hand, go outside and toward the firing range. The access to the generator room is down a set of stairs on the side. Go inside and forward. Just hack the terminal, it should be at the "easy" level, and open the containment area. Roy will come running up to the metal screen and thank you. He'll then ask you to come around front for your reward.
Go back out and to the front to receive your very own ghoul mask. Don't listen to him, since it will always work regardless of how close you are to the ghouls.
The rest is up to you. Just go inside and watch the security forces fight the ghouls. There should be more than enough ghouls to help Roy take the lobby. The second floor is a bit tougher, since Dashwood is absurdly strong. He'll probably kill about 15 ghouls before they overrun him. It's actually fun to reverse pickpocket better weapons onto him and watch the fight. As long as you don't talk to the people, they won't go hostile. Finish it up by going to the top floor to watch Tenpenny die. Wait for about 72 hours and Roy will take over the tower and Tenpenny's old spot on the balcony.