Your best bet is to start with the skin that comes with Road Runner. Load those images up in Gimp and change them around to get a look that you like. After you are satisfied with the images, fire up the skin editor. It is pretty straight forward to use. You can then drag the buttons, labels, indicators ect with the mouse, resize them ect.
This is how I started, with the skin that used to come with RR, the BMV2 skin. After tinkering with the skins, moving things around a bit, it all came together, and at that point started designing a skin from scratch.