What I did was found a pattern for a t-shirt online and altered it to my needs. Needs to open in the back and have the short quilted sleeves. Beware of the arm hole on your t shirt pattern, they often make it too big so shrink it down so just your arm will fit through. I also left the bottom a little long until I was able to figure out how short it needed to be as it should only continue about a 1/2 inch after your bottom plate. You'll also want to put some batting in it to give your vest some thickness, I have batting between two layers of fabric through my whole vest, gives it a nice padded look. Also, start with white or off-white fabric, it will save you time getting anything grey to lighten up to the ROTJ color. Hope that helps some, good luck!
Edit: One more thing, this takes a lot of patience and adjustments to get it right and to fit you correctly. Remember, always give yourself more fabric than you think you'll need; you can always take it away, you can't add it.