Wow, this is a great topic. The worst part of building for me would have to be painting the cabs, hoods, sleepers, etc. "bodies". I'll get the body work all done, sanded real nice, everything is straight, and just the way I want it, then I'll shoot some paint on it and it will not come out the way I expected it to. Orange peel is the biggest thing to try and avoid when painting. I have gotten better over the years, with all the tips and tricks I've learned from friends. I've had cabs/hoods not come out right the first time and strip them and repaint them 2 or 3 times before I got it right! Ahh! It's just like anything else though, the more you do it the better you will be at it.