Star Wars Galaxies you could place houses anywhere with exception of some event planets and even create cities.

But you must take note of that todays games and areas is seriously small in comparison to SWG, which is also sad, if you broke your hoverbike (swoop) far out it was a seriously long walk back.. but again they could make huge areas 20 years ago, but not today.

Would love if they implented that housing system, also the housing system in SWG is some of the best I have ever seen... you can place items anywhere... lift them from the ground rotate in ANY angle and more... houses where built by crafters that then could get placed the entire thing to craft required logistics as well as factories to serie produce sub components.

I don't think something like that would ever happen again in an MMO... the system where players could build cities and elect mayors of them as well as having a city militia and built in tax systems as everythign required maintenance to keep running.