Player houses can be built almost anywhere. Anywhere that it is physically possible, although in some areas NPCs may not allow it at all.
You can’t build a house in the ocean, in a swamp, or close enough to another building to undermine it’s foundations.
To build a house you need a lot of wood and stone, and for some things the services of an engineer, and as many helpers as you can get. The more people available to help, the faster a structure can be built – and engineers build a lot faster than unskilled people.
Houses can be built in a variety of styles and sizes. Once built they can be changed inside with regard to flooring and walls, and can even be decorated with a wide variety of items, some useful, some purely decorative.
Chests can be used to store items and can be locked. Anyone with a key can open a chest and take things out or put things in. Items inside chests will never expire as items simply dropped on the ground will.
Anyone with a house key can open the door, and leave the door locked or unlocked. Anyone can open an unlocked door. To some extent a key signifies ownership of a house – though more than one key may be created. Keys are items that are carried and are dropped on death like anything else, and can be traded to other people.
Being in a house gives logging off a much greater degree of safety, but logging off in an ordinary house does not change the rules.
A deed to a house may be purchased from any nation by anyone with at least standing zero to that civilization. A deed can be used by anyone, not just the purchaser.
When starting to build a house, the builder uses the deed to claim land and place the foundations of the house. This gives legal recognition of ownership of that house. A deed plate will appear on the house outside the front door and just inside it. Ownership can be controlled at the deed plate. The owner can list anyone they wish as a friend of the house on a deed plate or as a co-owner, and even transfer full ownership of the house to someone else.
Owners and co-owners of the house can change the house locks, invalidating all existing keys, as well as create new keys. Only the owner can add people at the deed plate or transfer house ownership.
Anyone listed on the deed plate can log off faster inside the house in view of the greater safety now offered.
Castles are large fortifications, in some ways similar to houses but on a much larger scale. They cannot be built from scratch, however the ruins of old castles can be restored by players.
Castles are the only buildable structures that can have walls raised to keep out other players, with mannable battlements.
Each castle location has an inner and outer bailey. The inner bailey controls access to the keep, while the outer bailey is large enough to build several houses and structures safely inside.
These buildings can be built by players but they are not really owned by them. Instead they are built after an agreement with a religion or the guild of bankers. Such buildings offer their services to all, not just their builders. But of course clever players may arrange to control access to the buildings in the first place.
It is considered that buildings are being maintained by those who live in them. If nobody has paid the upkeep costs within a certain amount of time then it will start to decay.