Mail Box & Door

For the mail Is it ok if you can make a mail box that makes the player that placed the mail box have a slot of land that is made with a block that marks the area you want to build your house in, I would also like a door with a key which works for the player that placed the door and if you click on the door while holding the key it will work for that door only and the player can give keys to other players so that they can access the house.