James Paddock - ANYONE can make a DOOM map.
Readyon - The Basics and Fundamentals of Doom Mapping
LEARN DOOM MAPPING! - Mapping With Dragonfly, Episode 1
DavidXNewton - David Develops Doom - The Visual Language of Doom Maps
MXDash - DOOM Mapping Tips and Tricks: Game Mechanics
decino - Analysis (Doom Mechanics)
Chubzdoomer - John Romero's Level Design Rules
Chubzdoomer - Sandy Petersen's Level Design
Chubzdoomer - ZDoom ACS Scripting Tutorials
Nirvana - How to Make a Doom Map That Looks Good
Doom: The Golden Souls (Remastered)
(note: this is a horror wad)
Power Pak - MyHouse.WAD - Inside Doom's Most Terrifying Mod
DavidXNewton - The Mysteries of myhouse.wad Explained (How it works)