Here is a quick guide for all the buildings in Ninja Kingdom.
The palace is the main component of your base. If your palace is destroyed, it counts as an automatic loss. Protect it at all costs if you would like to win more trophies. However, if you want to get a free shield, put them outside your walls.
This will determine how many buildings you can build at any given time. I recommend you have at least 3.
The clan hall will allow you to have troops to support you during defenses. You get more troops by contributing gold to your clan. When you contribute a set amount of gold, you unlock extra bombs or walls that you can use for defense.