A popular robot for fun is the Quadcopter, a robotic flying machine that has four helicopter-like rotors, and can do all sorts of aerial maneuvers by varying the speeds of its rotors. And some time ago, someone taught them to build building frameworks. Wait, what?
Discovery News reports that the University of Pennsylvania has developed Quadcopters that can manipulate plastic rods with a magnet on one end into the framework of pretty much any building. The metal end of one rod connects to the magnetic cube on the other, to form extremely solid building frames. Presumably one could finish it off with walls and floors that also attach to those magnets.
Already, people are imagining using these to throw up buildings in a hurry in places where it's impractical to take human construction workers. War zones. Mars. Antarctica. The quadcopters will cheerfully work in all of those places. And given a solar-powered charging station, they can work until they run out of parts. Admittedly, they sound like a swarm of angry bees from hell and being in the vicinity of them would be quite unpleasant, so I don't imagine them working urban construction anytime soon. (Especially because scaled up to the point where they'd make human-sized buildings, the noise would certainly rupture your eardrums.)