The Storehouse can be found on Home Island, and will always remain there.
Upgrading the Storehouse will increase the number of slots you have for storage.
It can be upgraded 6 times throughout the game, with each upgrade requiring a different set of items.
For more info on upgrading the Storehouse, check the guides we have posted to our official Facebook group and Discord channel.
To learn more about building, check out the Crafting Stations section!