I wanted to build something complex, interesting and offered a canvas for lots of textures, surfaces and shapes. I didn't use a concept, but looked at a few real-world references to get going.
Someone asked me what the theme was, and I replied that it's somewhere between Buck Rogers, Call of Cthulhu and NAZI weird-science/Weird Wars where it would be at home against strange conspiracy stories of Werewolf troops and reanimated zombie soldiers. It's not steampunk, as much as that's the first thought, but powered by hard radiation, unknowable eighth-dimension science and ghost-stuff. It shoots through schools.