On another online game (which unixmad used to play
), for houses (or big amounts of resources or other objects you could not carry with you etc.), you buy a deed from an NPC. You go where you want to place a house, then you double click the deed and thus place the house.
That is probable the case here, too, but only for transforming your personal house into a public shop of some sort. I think houses are going to be built by bringing lots of stones to the desired location.