District buildings

District buildings is a new concept of the game (that was introduced on early 2020). Those buildings are quite big (10x10) but can store other building inside them, hence giving you more space in your castle or OPs for decoration items that can increase your public order (PO). There are 3 types of district buildings: Military, Trade and Inner. Each of them can store different buildings. All district buildings when being bought (or when you win them as a prize) has a basic capacity of 2 building (at level 1) and can be then upgraded to a maximum level (that vary) to hold all possible buildings.
Here is a list of all buildings that can be stored in each of the district buildings:

Upgrading district buildings

To upgrade a district building you will need to have enough "Construction Tokens" & "Upgrade Tokens". Those are not so easy to obtain and in addition some of the upgrades, especially at high levels takes days to complete. For those reasons, it is recommended that you always check if there are buildings outside the respective district before you upgrade it.

All district buildings has the same upgrade cost & time. Here is the detailed information 

Types of district buildings

Military district

The first district building that was introduced in early 2020. It can contain up to 12 buildings (therefore, can be upgraded to level 11). You may purchase it  with 150,000 gold pieces at the "Master Blacksmith".

Inner district

The 2nd district building that was introduced in late 2020. It can contain up to 14 building (therefore, can be upgraded to level 13). As for now, you may get this building if you make the "top 250" on one of the monthly events (e.g. "The emerald trail", "Grand Nobility"). However, it is expected that it will  be available to purchase with 150,000 gold pieces at the "Master Blacksmith".

Trade district

The 3rd district building that was introduced in early 2021. It can contain up to 12 buildings (therefore, can be upgraded to level 11). As for now, you may get this building as the 1st prize on one of the monthly events (e.g. "The emerald trail", "Grand Nobility"). As for the previous district buildings, it is expected to become the "top 250" prize on one of the monthly events, and later to become available also for purchase with 150,000 gold pieces at the "Master Blacksmith".

Moving district buildings

As for the 31-March-2021 update, you will not be able to manually return to your storage any districts (and Relic) buildings. This means that you will not be able to move them from one outpost to another anymore. Only when an outpost is conquered those buildings will automatically return to your storage. In addition this upgrade is also preventing upgrade of relic buildings placed in outposts where their resource is not produced (ie. the relic woodcutter in an outpost with productivity for stone will no longer be upgradable).