gnome-session-save --shutdown-dialog in gnome 3 not there
 

I have been trying to add a shutdown button in debian wheezy gnome 3 but the "gnome-session-save --shutdown-dialog" is not available even in root terminal. I prefer to shutdown from within the window with power button icon instead of logging out or opening terminal.
Is there a way to put the script in for gnome-session-save --shutdown-dialog?

Press Alt while in the user menu.

Alt does nothing Alt+F2 opens command but the command gnome-session-save --shutdown-dialog returns "command not found".

I just figured out what you meant by the user menu. Clicked on it then pressed Alt & there it was, Poweroff.
So there is no need to create custom icon.