You can store more than ever with the new Storage Expansion! Please find a quick guide on how this feature works below.
You can now increase the capacity of your Storage Buildings. Each of your storage buildings can be upgraded twice. The first upgrade will provide you with 5 extra storage and the second upgrade will provide 7 extra storage. The two upgrades will give you 12 extra storage spaces in total.
There are two ways to expand your Storage.
1)The first way to expand storage is to pay Farm Cash. If you wish to purchase the storage upgrade with FarmVille cash (10 FC), you can do so by clicking the “BUY” button.
2) Alternatively, you can hold a Barn Raising, by clicking the “Expand Storage” button. After choosing to expand your storage, you will receive a pop-up, clicking the “okay” button will allow you to post a feed to your wall.
After posting your feed, you will have 3 days to have 10 of your friends click on your feed. (Each of your friends can help ONCE per day (24 hours). Up to a total of 3 times (once per day) during the Barn Raising. This means you do not necessarily need 10 unique friends.
When you click on a friends feed asking for Barn Raising, you will receive 100 coins.
If you wish to “give up” on the barn raising, you can click the “GIVE UP” button and the barn raising will cease.Please keep in mind that you can only raise 1 storage item at a time.
If you do not manage to get 10 clicks on your feed in three days, you can purchase the storage upgrade at a discounted price equilavent to the amount of clicks you recieved.
The closer you manage to get to 10 clicks, the cheaper it will be to purchase with Farm Cash.”
Source: Are you SATISFIED with 200 Items in your store? How many days do you need before asking another upgrade in FarmVille Storage Capacity?