Minecraft wiki entry for End_City, associated text: Base floors, which are empty floors found at the base of every city; they are three stories tall, with each room wider than the one below it.
Banner rooms that have banners hanging on the outside, and a shulker attached to the ceiling.
Small rooms that have nothing in them at all.
Large rooms that have precarious parkour-like staircases often leading up to another tower or a loot room.
Loot rooms that consist of two chests with valuable loot at the end of a small parkour area; some rooms may have one normal chest next to an ender chest instead.