Buildings in kingdom to upgrade weapons (ballistas, catapults, cannons, trabuchets), a building for all those.
A building for upgrading shields.
A building for upgrading troops.
It can be made as choices like if you invest in thianupgrade you can’t upgrade that, etc… you can upgrade for weapons stuff like, damage, ranve, cooldown maybe, speed of projectile etc.
For shields… shield size, shield speed of deployment, shield active time, etc
For troops, more HP, or more damage, or more speed, attack speed… etc…
All based on choices… you can’t upgrade all… that should promote build diversity