The Decoration Storage Shed costs 620 coins, and then requires you to collect a ton of building materials:

• 5 Door Hinges
• 5 Door Locks
• 5 Floor Drains
• 5 Light Bulbs
• 5 Plywood Flooring
• 5 Roofing Felts

As you might expect, earning these items comes via a combination of general requests posted on your wall and individual requests sent out to friends. You can purchase all of the items outright with Estate Cash, if you'd rather not bug or wait for your friends to help, but either way, your storage will be limited to start. That is, you'll only have 16 storage slots for decorations when you've finished it off. Don't worry though, even though you've stored a decoration, you will not lose Estate Points; you'll simply free up space on your land that will allow you to place even more decorations or buildings to unlock even more scenes in Hidden Chronicles. There are four quests that go along with the construction of this Decoration Storage Shed.