Making a Map for Doom/Doom II: A Guide

Making a custom level for the classic Doom games is a simple process.
  1. Accept the help of Ultimate Doom Builder wherever possible. Don't forget; it's the only actively-maintained option.
  2. Get a PhD. in the behaviour of node builders.
  3. Get told that you should have made your map less difficult.
  4. Get told that you should have made your map more difficult.
Got all that?