Done some doodling for the areas, found it hard to get started digitally so I just doodled on some paper. However, I did an orthographic of an idea for the basement area;
Going for a grungy look, with a mild sense of it being "lived in" by squatters and addicts. The graffiti/wall writing would be in colour and more widespread, now that I look at black is the wrong colour for it.
Also, I listed the textures we'll need for the BSP. I've got a sneaky feeling that these can't be all the ones we'll need, but I did have a walk through with a notepad and these are the only ones I could really see. Probably go back after the BSP is textured and see if I missed anything.
The first is for the basement; this isn't referenced from Queens so there's some freedom there. The second is a plain white wall which is featured around. Third is an alternate version of the Atrium wall, which is in the connecting area. After that, the flooring for the corridor, then the roof texture on the top floor, followed by the basement stone/concrete, then the green carpet on the top floor. The next row starts with the tiled white brick featured in the machine hall, then the green brick that's featured once in the Atrium, then the brown brick that features heavily in the atrium. The stripy floor that follows in used in the connecting room, then the diamond floor of the Atrium.
Like I said, feel like I've missed something, but this should do.