This is how it works, most of the time.
A developer, builder, business owner, homeowner, someone decides they want to construct a building. They hire an architect or engineer to draw up some plans.
The design professional (could also be a contractor) finds out where the building is going to be and the general dimensions of the strucutre. This information is plugged into the requirments found in Chapter 5 of the building code. Per this Chapter, the area and height of the building will likely dictate the type of construction as defined in Chapter 6. Mix in the requirements of Chapter 3, and you got yourself a building with defined dimesions, loaction on the lot, fire ratings, construction type, and occupancy type.
The rest are details.