Building mode or build mode is used when players want to access their Player-owned house to start constructing rooms, building furniture, etc. This feature can be accessed from the Options menu in the main game interface. Once "House options" button is chosen, players can toggle Building mode ON and OFF. Build mode is not safe and can be raided by pkers. A pker attempting to raid a player in build mode will kick the players out of build mode. It is not possible to lock the portal either.
When building mode is OFF, house owners can invite friends to visit their houses. Anyone visiting the house will only see furniture that has already been built. Owners can host parties, duel with others, and serve tea while in this mode. Basically, in this mode, entering the house will be the same as entering any other house or building in DarkScape. By default, building mode is set to OFF. Familiars are not allowed to be out in building mode.
This article incorporates text from the RuneScape Wiki which is also licensed under CC-BY-SA.