Each IWAD into a 9-map episode.

You can use 9 regular maps, or 8 regular maps and one secret map or any other way you see fit, just use 9 or less levels.

Ultimate Doom:
E1M1 Hangar
E4M9 Fear
E2M7 Spawning Vats
E2M2 Containment Area
E3M7 Gate to Limbo/Limbo
E3M6 Mt. Erebus (Secret exit)
E4M5 They Will Repent
E4M8 Unto The Cruel (Last map)
E4M2 Perfect Hatred (Secret map)

Doom 2:
MAP01 Entryway
MAP03 The Gauntlet
MAP14 The Inmost Dens
MAP11 Circle of Death
MAP15 Industrial Zone (Secret exit)
MAP20 Gotcha!
MAP29 The Living End
MAP30 Icon of Sin (Last map)
MAP23 Barrels O' Fun (Secret map)

TNT:
MAP01 System Control
MAP10 Redemption
MAP17 Processing Area
MAP15 Dead Zone (Secret Exit)
MAP13 Nukage Processing
MAP16 Deepest Reaches
MAP24 Quarry
MAP29 River Styx (Last map)
MAP32 Caribbean (Secret map)

Plutonia:
MAP02 Well of Souls
MAP08 Realm
MAP10 Onslaught
MAP12 Speed
MAP16 The Omen
MAP19 NME
MAP29 Odyssey of Noises
MAP31 Cyberden (Last map and secret exit)
MAP32 Go 2 It (Secret map)

Chex Quest 3:
E1M1 Landing Zone
E1M3 Laboratory
E1M5 Caverns of Bazoik
E2M3 Chex Museum
E2M4 City Streets (Secret exit)
E2M5 Sewer System
E3M4 Provincial Park
E3M5 Meteor Spaceship (Last map)
E2M2 Cinema (Secret map)

I haven't played any other IWADs, I am however planning to play through more in the future.