Heh, I actually thought of doing that as I found it a painful process to constantly have to refer to other UI's or guess-and-check to get things down.
I made a couple templates for my own use, but most I never bothered to save after I was done with them, since I could just use my own art as reference.
One of the few ones I still have are the large tabs for example.
You can see my tab on the foreground and the left, center, and right pieces as the red and yellow. I just drew the whole tab on the template and then cut it up.
I'd consider templating the whole thing as I know how much of a pain it is to figure it all out.