Wood is the most basic construction material, used in almost all upgrades and constructions.
The only time Wood is not used in a construction or upgrade is after you have unlocked Stone. After that, the Sawmill no longer takes Wood to upgrade.
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 Wood Storage is made of wooden planks on vertical supports, with a crude one-sided fence.
At level 2, the Wood Storage gains another fence at the opposite side, and the support on the bottom is now moved to the side.
At level 4, the Wood Storage gains a wooden roof with wooden support beams. The support beams are reinforced with stone at the bottom.
At level 5, the wooden support beams are replaced with stone supports, and the top plank on the roof becomes a lighter color.
At level 6, the Wood Storage gains a corrugated metal roof. The support beams are changed to steel.
At level 7, the metal along the very top of the roof becomes a darker color, and a dark metal base is added.
At level 8, the corrugated metal on the roof is replaced with flat, metal sheets and a dark colored metal patch. The base is further reinforced.
At level 9, the metal patch is replaced with a vent, and the corners of the roof gain small pieces of metal.
At level 10, the vent is replaced with a fan, and all the storage's edges are reinforced further. A caution design is added to the edge of the storage area.
Trivia
The Wood Storage has the highest amount of visual upgrade differences within the economy building category.