As the serving head of the Inquisition, you can customize Skyhold in different ways – ranging from windows to drapes and decor to throne. To unlock this, you need to complete Avvar Tribesman ...

Once you reach Skyhold in Dragon Age ... Inquisition Trappings' quest. To complete the quest, you simply need to head to the Undercroft (through the door to the right of the Skyhold throne ...