Tip: Building new Holdings

An often-overlooked feature for new players is the ability to build new holdings in your (and your vassal's) provinces. These are the empty slots next to the castles, bishoprics and cities already built.

Here are some tips as to the best way to utilize these extra slots.

Cities:

You want cities, cities are the best. You want every open slot in every county you personally own to be filled with cities. The ideal county has one castle (your holding) one bishopric (required) and the rest cities. Cities provide the most tax income and are much more reliable than bishoprics (who might give their taxes to the pope if they don't like you).

Once you have upgraded all the economic buildings in your personal holdings, make it a point to fill your empty slots with cities to further boost your income. Extra cities in your capital also mean room for more universities, which means better tech for you.

One last tip: When a city is finished, go ahead and build one of the 100-gold economic buildings there before handing it off to someone. That will help the mayor kick-start their income and give you more in the long run.

Castles:

There is only one reason I can think of to build a barony level castle: Landing a claimant. If you have someone in your court who has a claim you'd like to press, you need to land them first. Otherwise they won't become your vassal when you win the war.

Rather than giving away one of your personally held counties, or going through the trouble of revoking a title to give it to the claimant, you can always build a brand new castle and give it to them once it is finished constructing. I highly advise to build these in your vassals' holdings if and when you need to build them at all.

Bishoprics

The only time I could ever see wanting to build these is if you really needed to make someone a bishop right now. The primary case for this is to remove a child from the line of succession (since you can't nominate children when in free investiture). This is an alternative to just revoking a bishop's title, where you value not getting that -20 vassal opinion more than the large chunk of gold it'll cost to build the holding. Like with castles, these are best built in vassal holdings as you want all your own slots to be filled with cities.

Parting notes This is written from a feudal catholic ruler's point of view. You can build cities in your vassal's counties, but I don't see this as ideal as you'll rarely get a return on your investment and just make your vassal richer. If your vassal gets wealthy enough, they might build their own holdings.