So far I remember the devs mentioning that you will determine the “function” of a building by what you are placing into it. So if you place a carpenter’s workshop into a room, this turns into the carpenter’s shop. Room means that you should be able to place more professions into a bigger building and you are not locking the purpose of a whole building by placing a workshop into a corner.
Other than that I think you determine other usages also by the items you place into it. If you put in there a stockpile and limit the resources to “gold”, here you go with a treasury… do the same for weapons and you might end up with an armory.
Not sure if the new construction concept or other considerations have changed that in the meanwhile.
@SteveAdamo … this one?