Iron is used to upgrade most higher level buildings.
Unlike some other real-time strategy games, if this building is destroyed during a battle, the attacker does not necessarily gain some of the Resources in it. The only way Resources can be taken from it is if the attacker destroys the Headquarters.
Upgrade Differences
Initially, the Iron Storage is a teal-colored iron repository with walls on three sides. The tops of the walls are reinforced.
At level 2, the Iron Storage gains an arched wooden roof.
At level 3, the roof is replaced with a metal one.
At level 4, the roof is rearranged so that it is even with the walls. The walls' reinforcing changes color.
At level 5, the stone base is replaced with a metal one, and the storage's edging becomes blue.
At level 6, a short ramp-like structure is added to the front of the storage area.
At level 7, the arched roof becomes thicker, and now has bolts in it.
At level 8, the storage gains two metal supports on each side.
Trivia
Iron is used in every high level upgrade except for the Iron Mine.
Sometimes, Villagers will carry resources, such as Iron, to a building being upgraded even when Iron was not required for the upgrade.
