The Fountainhead

Howard Roark (Gary Cooper) is an individualistic architect who follows a new artistic path in the face of conformity and vulgar mediocrity.
Ellsworth Toohey (Robert Douglas), an architecture critic for The Banner newspaper, opposes Roark's individualism and volunteers to crusade in print against him. The wealthy and influential publisher, Gail Wynand (Raymond Massey), pays little attention, but approves the idea and gives Toohey a free hand.
Dominique Francon (Patricia Neal), a glamorous socialite who writes a Banner column, admires Roark's work, and opposes the newspaper's campaign against him. She is engaged to be married to an architect herself, the unimaginative Peter Keating (Kent Smith). She has never met or seen Roark, but she believes that he is doomed in a world that abhors individualism. Wynand falls in love with Francon and exposes Keating as someone who values a big opportunity more than her.
In the meantime, Roark is unable to find a client willing to build according to his vision. He walks away from opportunities that involve any compromise of his standards. Broke, he takes a job as a laborer in a quarry. The quarry belongs to Francon's father and is near their summer home. The vacationing Francon visits the quarry on a whim. As Roark drills into the stone, Francon spots him and watches him work. When he sees her they openly and repeatedly stare at each other.
Francon contrives to have Roark repair the fireplace in her bedroom. Roark mocks the pretense, and after the first visit, sends someone else to complete the repair. Expecting Roark, Francon is enraged and returns to the quarry on horseback. She finds Roark walking nearby. He again mocks her and she strikes him with her horsewhip. In the evening he invades her bedroom, forcefully embracing and kissing her as the film fades to black, implying sexual intercourse.
Back in his small room, Roark finds a letter offering him a new project. He packs up and leaves. Francon goes to the quarry and learns that he quit. The boss offers to find out where he went, but she declines. She has no idea that he is Howard Roark, the brilliant architect.
Wynand offers to marry Francon, even though he is aware that she is not in love with him. Francon defers the offer until she feels a great need to punish herself. She learns Roark's true identity when they are introduced at the party opening the new building that Roark has designed which The Banner has campaigned against. Francon goes to Roark's apartment and offers to marry him if he gives up architecture to save himself from a hopeless struggle. Roark rejects her fears and says that they face many years apart until she overcomes the error of her thinking.
Francon finds Wynand and accepts his previous marriage proposal. Wynand agrees regardless of her true feelings or motives. Wynand discovers Roark as an architect and hires him to build Francon a secluded country home. Wynand and Roark become friends which drives Francon to jealousy over Roark.
Keating has been employed to create an enormous housing project. It is beyond his skill, so he requests Roark's help. Roark says that if Keating promises to build it exactly as designed, Roark will design the project while permitting Keating to take all the credit. With prodding from the envious Toohey, the firm backing the project decides to alter the design presented by Keating. Roark decides, with Francon's secret help, to rig explosives to the project and destroy it. Roark is arrested at the building site. In order to demonstrate Roark's guilt, Toohey pressures Keating into privately confessing that Roark designed the project.
Roark goes on trial. He is painted as a public enemy by every newspaper apart from The Banner, where, breaking with previous policy, Wynand campaigns publicly on Roark's behalf. However, Toohey has permeated The Banner with men loyal to him. Toohey has them quit and uses his clout to keep others out. He leads a campaign against The Banner's new policy that all but kills the paper. Faced with losing the enterprise, Wynand saves The Banner by bringing back Toohey's gang to join the rest of the public in condemning Roark.
Calling no witnesses, Roark addresses the court on his own behalf. He makes a long and eloquent speech defending his right to offer his own work on his own terms. He is found innocent of the charges against him. A guilt-stricken Wynand summons the architect to his office. He presents him with a contract to design the Wynand Building, to be the greatest structure of all, with complete freedom to build it however Roark sees fit. As soon as Roark leaves the room, Wynand commits suicide.
In the final scene, Francon enters the construction site of the Wynand Building, and identifies herself as Mrs. Roark. She rides the elevator towards Roark, awaiting her atop his magnificent new building.

Question: Where is Roark arrested?
Answer: The building site