All other major components such as masts, deck furniture, stern galleries and figureheads are designed and fitted on the computer model before any 'real' construction is begun. Notice also how normally only half the ship is designed, symmetry prevails in pretty well all ships.
This is also very similar to how a sailing ship was designed 300 years ago, instead of a 3-D computer model, they would have had a wooden scale half-model of a proposed ship, showing the hull from stem to stern. It was made in layers, which when taken apart, served as sections for the full scale plans.
Again we have it easier, once we have a 3-D surface- or solid-model of the hull we can let the computer do all the work to get any section instantly. The geometry shown above is that of our half-model of the USS President. We then can take any section we need, and print or plot it to scale as a template for a rib, frame or bulk-head.
Half breadth plan. The curves shown below in light blue are the waterlines, which are curves in a horizontal plane following the shape of the hull; cross-sections are shown in gold.