I usually make it up as I go but I really should not do that. I do keep mental notes before/during mapping on how I want the map to progress, how rooms should look, and how combat encounters should be but that's the most I'll go.
I recall reading about how Quake and even Doom 3 shared a singular function from the Doom engine but aside from that they're entirely different.
Summoning @Quasar as I recall him making a post about it.
Super Metroid and Prime 2. I'm currently going through the Metroid series as I just beaten Prime 1 (which was phenomenal game and probably one of my favourite games of all time)
Hate to announce this so late but I resigning my spot for X. I've simply just haven't had the time to devote to it due to school and other factors. Sorry.
Though skimming through the the thread, the maps look great so far! Hoping for a fun and wacky mapset at the end :p