They've improved the build mode for the Sims, and you'll see exactly how it works in this new trailer for the The Sims 4. Instead of messing with little individual pieces, you can now simply slide around whole rooms, with the system making adjustments in real time to fit that room where you'd like, with quick click-and-drag resizing. Note the drag/drop roof work. You'll be able to piece a building together very quickly with this new system.
The Sims 4 is currently under development for PC. Wait to hear more about it at E3 next month.