There are no ‘unecessary buildings’ in the game. Every player at the same level can build the same amount of each buildings. You have empty spots, so you have not built all your buildings.
Per @Coppersky 's guide:
After the tutorial you have 5 slots available to build a farm, iron storage, and food storage.
At level 3 you can add: farm, mine, food storage, forge.
At level 5 you can add: house, farm, training camp, iron storage.
At level 8 you can add: forge, iron storage, farm, mine.
At level 11 you can add: farm, training camp, house, food storage.
At level 15 you can add: farm, mine, iron storage, forge.
At level 20 you can add: house, training camp, farm, food storage.
so how many iron storage do you have?