The buildings section allows you to place any in-game building already, plus the addition of some editor-only buildings such as Outlaw Camps. The buildings section consists of two sub-sections, "Buildings" and "Editor-only Objects". These are the available buildings:
Keep
Food Buildings
Resource Building
Housing
Town Buildings
Honour Buildings
Weapons Workshops
Military Buildings
Statues
Rewards
Punishments
The following items are from the Editor only section:
Ruins
Signs
Gravestones
Debris
Estate Halls
Non-Player Buildings
Bridges
Cliffs
Logs
Rocks
Fires
Disease
Effects