Most good stories start with a fundamental list of ingredients: the initial situation, conflict, complication, climax, suspense, denouement, and conclusion. Great writers sometimes shake up the recipe and add some spice.
Initial Situation
The first section of the novel parallels the start of Keating and Roark's respective careers. When Roark finally strikes out on his own, it represents a turning point in the action.
Conflict
After setting up Roark's career and the complications that come up at work, Rand introduces love to the mix. At this stage in the game, Roark is battling for both his professional and his love life.
Complication
Roark and Dominique start a complex emotional and physical affair in secret while Dominique grows further connected to Peter Keating and Toohey at The Banner. The cast of characters is, at this point, all assembled, and rivalries start to become apparent.
Climax
Roark goes to trial over the Stoddard Temple debacle (or disaster) and Dominique marries Keating. Everything sort of blows up in people's faces here as Roark's career and personal life becomes epically stormy. The events in this section impact everyone in the novel, though, not just Roark.
Suspense
Rather than resolve things, Rand makes them more complicated by having Roark continue to struggle with his career and by having Dominique move on to another man: Dominique and Keating's marriage disintegrates and she ends up leaving him for Gail Wynand.
Denouement
This book is so long that it has a series of climaxes and denouements and build-ups to new conflicts and climaxes. However, Roark's commission of the Cortlandt House and Wynand and Roark's bromance signal the wrap-up of the novel and pave the way for the conclusion.
Conclusion
Roark blows up the Cortlandt House, goes on trial, and wins both the trial and Dominique. The end.