In a recent article at MMORPG.com, they run down the details of each of these guild city buildings, and their biggest advantages. Also in this article are some details on guild leadership itself. In order to create a guild city, your player will need to be a guild leader, level 40 or higher, and have a guild membership of at least 24 players. You will then have the choice of 3 environmental locations currently for your guild city. Let the land-grab begin!