Ubuntu Guide posted a simple and brief tutorial to show you how to add 'Open As Root' to Nautilus context menu in Ubuntu 13.04 Raring

The Nautilus has upgraded to 3.6.x in Ubuntu 13.04, so that it's a little different. Now the Nautilus scripts should be placed under "/home/$USER/.local/share/nautilus/scripts/"

  Open As Root / Administrator in Ubuntu 13.04