This highly classified and immense project is still under construction at this time.  Only the highest ranking of imperials are even aware that it exists.  Even though it is many years away from completion, there's still plenty enough of it to allow for living quarters and workers.  Be warned, as the 501st can tell you, this place is a boredom nightmare for a soldier because of endless drills, tests, and one military director with a white cape that's looking for anything to further his ambitions, and also yells a lot.