Boba Fett's helmet seems to be a popular choice for first time pep builders on these forums. Having been a long time fan I choose Boba Fett's notorious bucket for my first build as well.
I recently stumbled across the art of Pepakura while researching different methods for my costume project.
My first choice of material was foam however and as you can see that horrid attempt just didnt live up to my standards. I used a PDO that was not firefek's and the contours just didnt work out once I got the bottom half of the bucket assembled.