To unlock the special rooms that need collection items, post the requests on your Timeline and your friends will be able to send you the items for free. Only 1 item per friend can be received.
Once you have collected all the items, the room will be unlocked and you will be able to enter the special room.
You can also unlock special rooms by using Facebook Credits.
You can help your friends to unlock the special rooms by clicking the Send Free Invitation to give them one item.