server/res/buildings/castle-2.xml

<?xml version="1.0"?>
<building name="castle" fort="yes" taxes="100">
  <construction skill="building" minskill="1" maxsize="10" name="site">
    <requirement type="stone" quantity="1"/>
  </construction>
  <construction skill="building" minskill="2" maxsize="40" name="fortification">
    <requirement type="stone" quantity="1"/>
  </construction>
  <construction skill="building" minskill="3" maxsize="200" name="tower">
    <requirement type="stone" quantity="1"/>
  </construction>
  <construction skill="building" minskill="4" maxsize="1000" name="castle">
    <requirement type="stone" quantity="1"/>
  </construction>
  <construction skill="building" minskill="5" maxsize="5000" name="fortress">
    <requirement type="stone" quantity="1"/>
  </construction>
  <construction skill="building" minskill="6" name="citadel">
    <requirement type="stone" quantity="1"/>
  </construction>
</building>