Everyone's Castle: Draw the Dragon's Nest at the Beginning

Billions of human beings traveled to another world, and everyone became a castle lord at the beginning, owning a castle. Each castle owner will randomly select a starting unit building to arm his castle. Recruit more troops, plunder resources, and dominate the world! Some draw paladins from the beginning, command an army of knights to crush all obstacles on the road, and rule the vast land. Some extracted goblin caves, developed castle trade, and became famous profiteers. Of course, more people only selected the most inconspicuous soldiers: goblins, lizardmen, skeleton soldiers... These people can only kneel in front of the powerful castle master and be slaves. But Li Ke is an exception. His unit building is the Dragon's Nest! Can breed frost dragons, hellfire dragons, undead dragons, dark dragons...