I come from the Ship building community and of course there is kit building with adding, kit bashing and scratch building. I try to 100% scratch build, but then I'm not making my own thread, brass, styrene and whatnot. Now I am starting to re enter HON3 with the 3D printing techniques I learned building ships. Beginning with vintage freight rolling stock I have copied the form of several model kits from 35 years ago. It seems to work out OK, I even made arch bar trucks, but they don't roll nearly as well as say Kadee or Micro Scale offerings due to lack of proper materials in the prints. Turned brass axels seemed to be better but not perfect. Making an operating coupler is currently beyond my skills. I will use PE brass if it is not in it's original application, for instance unfolded floater nets used for gratings or vent screening. Build as much as you can if that building ives satisfaction. A diverse hobby, so one should have time to achieve and enjoy operation!
Cheers: Tom