Joe Johnston is a director now (The Rocketeer, Jurassic Park III, Jumanji, and Captain America: The First Avenger), but he used to be an accomplished storyboard artist. When he was planning on quitting LucasFilm Ltd. Lucas asked him to work on the designs for the bounty hunter using McQuarrie's rejected Darth Vader designs.
During pre-production for Star Wars Episode V: The Empire Strikes Back, Johnston was responsible for the design of Boba Fett's distinctive armor and equipment. He worked alongside artist Ralph McQuarrie to develop the unique look for the bounty hunter, which was in fact derived from the early concepts of Darth Vader. - starwars.wikia.comThe Boba Fett cosplay site "The Dented Helmet" has a great gallery featuring tons of concept art for everyone's favorite bounty hunter. It's amazing to see how specific Johnston's drawings are about the armor. I figured they just threw stuff at it till it looked good.
First, McQuarrie's illustrations.
TheDentedHelmet.com for the rest.
As always make sure you check out McQuarrie's site RalphMcQuarrie.com.