/vr/ - Retro Games

>>3297327
You should start out with a theme or idea what the place is supposed to represent, and work from there.
Like ex. tech-base, what could there be?
- A reactor
- Warehouse
- Server-farm
- Laboratory
- Cistern / nukage pools
- Garden
- Dark underground tunnels

Although I'd recommend more focused idea, though, so you can visualize the sort of places you want. Sticking to some color (ex. two main colours), material ( wood / stone ) / shape-schemes ( very round corners? ) will help you then texture and detail the areas.
Areas don't have to make real sense, because real-life buildings are sort of boring from Doom's perspective.