This item allows you to change the appearance of your Barn while added 5 more to your animal limit. This item is available for 500 MC from June 23-July 7, 2011. The description reads "Let pirates take over yer barn and they'll increase yer animal limit by 5!"
You will only see the Pirate Barn in the shop if you have your Barn fully upgraded.
Once you purchase the Pirate Barn it shows up in your storage. To use it go to your storage and click the Use button. This will change the skin of your barn to look like the Pirate Barn. If you want to go back to the old style Barn simply click Use on the old Barn in your storage. Removing a barn skin or keeping it in storage will not affect your animal limit.