In maybe one of the greatest updates ever, FarmVille added DOUBLE storage on April 27th, 2010.
Yay for more storage! Thank you for listening to all of us begging farmers. Your storage capacity is now at 200! Originally, maximum storage was 100 items.
You have two options of upgrading your current storage system. The free option is holing a good old fashioned Barn Raising party and enlisting the help of your FarmVille neighbors to upgrade your barn. The other way is directly purchasing the storage expansion with farm cash, which is available in the FarmVille Market.
More details from FarmVille Community Manager Lexilicious:
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.