At Factory OS, apartment complexes are constructed room by room. Modular units are moved along on an assembly line: floors, dry wall, windows, then electrical, counters, and so on. When the units are completed, they are trucked to the construction site, and assembled like legos.
Ask a developer. Berkeley can be a notoriously difficult city in which to do business. Like many Bay Area cities, there are zoning issues, the Planning Commission, environmental impact studies and community resistance. And then there is the permit process. All of this requires a vision and endurance.