@DoomGappy Thanks for making such a cool guide! I tried to get into making doom maps a couple years ago but never really stuck with it, this was really helpful for a beginner. Having a lot of fun making my first proper map, I'll post it here when I'm done. Would definitely be helpful to include something on teleporters in the guide, that's something that confused me a bit and seems like a really useful tool for mapping that gets used a lot.
Here's a useful (and short!) video I found on making a teleporting monster closet:
https://www.youtube.com/watch?v=kFU9zUZuU6M