Exchange Server 2013 SP1 - How to create Resource Mailbox on powershell?

Hi,

I'm having a hard time trying to create a resource mailbox. The "Resource" page on ECP doesn't have the option to create (probably after the SP1 update deploy) so I'm trying to create on Powershell. The problem is that the help examples doesn't work, and I can't find it online either. It seems that with SP1 the command or the parameters changed.

Here's an example (get-help new-mailbox -examples): 

New-Mailbox -UserPrincipalName confmbx@contoso.com -Alias confmbx -Name ConfRoomMailbox -Database "Mailbox
    Database 1" -OrganizationalUnit Users -Room -ResetPasswordOnNextLogon $true

A parameter cannot be found that matches parameter name 'UserPrincipalName'

There's a lot of parameters that cannot be found. Any help would be much appreciated.