There are options in there for buildings such as the Chamber of War, Ballista Towers, and a Great Hall, but to start taxing your citizens, you are going to need to build a Throne Room. This tab holds all the buildings associated with constructing, upgrading, and maintaining your Castle Keep. If you look at your building menu tabs at the bottom of the screen, you will see the Castle Tab. As you place an upgrade in your city, your castle also gets bigger. Instead, upgrading your castle means affixing add-ons onto your castle. Upgrading your castle doesn't necessarily mean building on your existing castle, although that does happen in due course.
How to Upgrade Your Castle in Kingdoms and Castles To be able to tax in Kingdoms and Castles, you need to upgrade your castle. These require gold to build and the primary way to get said gold it through taxing your citizens.
They all cost zero gold to build, but early on, your residents will start suggesting that you build things like Churches. These are your houses, bakeries, barns, windmills, etc. So, you've built up your city as far as you can using the 'free' buildings during the initial part of the game. Related: Kingdoms and Castles Achievements Guide
