These are classified as special buildings because they can not be build or destroyed.
The basic buildings are where you get your start on creating your settlement and you should never under estimate the importance of these buildings in your economy.
Intermediate buildings help develop the basic elements you will need for war with your enemies and support your growing islanders goals.
Advanced Buildings are a bit more powerful and take advantage of the better consumables you are starting to obtain to make higher grade products.
Expert Buildings are the current pinnacle of Settler technology and are hard to obtain due to their high level but the powerful war weapons they provide will put any enemy to a quick end.
Exotic Wood Sawmill
Tightly Sown Wheatfield
Additional buildings available for purchase from the Architect category at the Merchant.
The following buildings can be found in the 'Epic' tab of the Merchant Chest, and require a high level.
These buildings are obtained as rewards for completing various adventures.
These buildings are made available during special events throughout the game.