This is really good to know that facebook started a messaging service. Many peoples are trying to get the new email id. But you are not able to create an email id till you have not been invited by the facebook. So, without wasting your time follow the steps and get the facebook email id.
Either wait for facebook invitation automatically or click the link facebook.com/about/messages/ and request an invitation. As shown below click green button in right bottom corner.
Wait for the facebook invitation. This may take time.
Go to you inbox -> claim you email id and enjoy.
Must remember that before creating a facebook email id you must have a facebook username.
One more think I want to share that techtree coducted a servey and found most for facebook user deny to use facebook as primary email id for more details visit http://www.techtree.com/India/News/Facebook_Email_gets_a_Cold_Response_from_Majority/551-113496-643.html