To store a building/decoration in the Building Storage, select any building/decoration you want and then click on Move, if it can be stored, a Store button should be available, simply click on it.
To place a stored building/decoration on your island, select the Building Storage and then click on Storage. From there, select any building/decoration you want from the menu and click on Install.
The Building Storage is a crafted building. In order to craft it, the player must pay not only the mana stones, but also the following crafting materials :
|Solid Iron Ore||15|
|Essence of Fire (Mid)||15|
|Essence of Fire (Low)||20|
- Note that (some ?) decorations stack. (Some more than the others)