This is how I made Zrdoom 5.0.

I first mapped out a grid of 10x10 64x64 grid square shaped sectors and tagged them all with unique tags and put in mapspots in them with the same tags as their parent sector sector tags.  I then filled in upper and lower textures for all 2 sided linedefs.  I then made a big script that altered sector geometry  to form randomly placed walls and refined that over 2 weeks to make height variation. It didn't look good yet...

By 1 week in I added in basic details and doors.  I then added in slopes and colored lighting.... I then after a lot of testing over 6 months  thought up a system to make height variation to allow for linedef texture alignment to be better by only using heights at 32, 64 and 128 units for heights.

I then made enemies teleport in to mapspots with a difficulty configuration setup to decide how hard the map would be.  I made it so harder enemies appear earlier in the map at higher mapspot tids and easier ones at lower mapspot tids. The difficulty of the enemies and what enemies to use was based on what difficulty configurtion you wanted... I programmed easy/medium (normal), hard (challenging), ultra hard (insane), beyond ultra hard (painful) and hell revealed 10 and slaughterfest 2069 for ultra hard maps for the last 2.

I then later on added in the ability for the map to recalculate on the fly on a timer and rebuild to form new maps to support the bot feature that allows bots to navigate the procedural maps on their own and made it so that the map would make a new map when crossing an exit teleport...

I at the end added in a setup to raise sector floors to make walls and used floor raising instead of the old system to lower ceilings to form walls. It was far easier this way to do skies, because lowering sectors with a sky to the floors puts skies on walls... I then rebuilt the whole thing to only have 13 such wall sector sets to make the bot not mess up as much.. This was the final version...