The Woody World Episodes/Maps (search Woody) have evolved a lot since I started mapping and learned a lot.
Now, as I make larger and more advanced maps, typically I
1 - Think of a concept (like climbing a mountain, stuck in a city, going down a river, etc.)
2 - Maps out the area/full map on paper with container placeholders for building/sections etc. Also place weapons and keys.
3 - Put the start and exit on the map. I like the player to be able to see the exit from the start if possible so they have an idea where they will finish
4 - Plan out a general sequence for the player to go (i.e. has to get Red key from this area or throw that switch before they can go to area B, etc. (although there are multiple paths to finish)
4 - Take each area/section and flush that out on it's own paper (i.e. with door, floors, hallways, secrets, etc.) often monsters as well
5 - Select textures for that area and build that area
6 - Populate that area with monsters and items/ammo
7 - Test that area
8 - Once 4-7 done for all areas, do a pass to ensure uniformity/texture alignment and sequence works
9 - Playtest entire map, take many notes on problems
10 - fix problems and/or monsters/ammo balance, step 9 repeat until perfect
11 - Once Episode is complete, release to beta testers
12 - fix reported problems
13 - release on DoomWorld!
In general, I avoid UAC tech base (too many out there) and hell/gruesome/corpses scenes/themes (yuk). I like more open spaces to run and explore multiple paths
Woody