You need to have WHM access to make cPanel skins.

WHM = Web Hosting Manager

It usually comes with VPS or Reseller hosting packages. Unless you can find a copy of the default cPanel skin to base yourself from from someone, you'll need to have WHM to get it.

But then again I never made a cPanel skin, so I'm not 100% sure if that's how to do it but I've been doing some research these past few days and that's what I came up with.

Just like forum skinning, there aren't any "tutorials" that are made, and learning how to skin from a tutorial isn't the best way, it'll teach you one way of making a skin and maybe cut your creativity that you would normally obtain by exploring and trying for yourself.

Good luck!