Hey thanks for the comments. I was getting worried that everyone gave up this thread.
To answer your question, the skybox is one of the stock skyboxes (sky_day03_06). Are you building cubemaps then restarting the game? That's what gets HDR working in most cases. The brick building's textures have been scrapped and replaced, I think it's in some of the screenshots somewhere.
As for the shadows from the grating, the method I used is to make the brush with the grating texture into a func_illusionary (func_brush works too with the right values) and to make rows of nodraw brushes in a grid inside the func_illusionary/brush. Having larger spaces between the nodraw grid compared to the texture looks a lot better than trying to match up the pattern perfectly. Lastly (if not already obvious) I set the lightmap number to a low number (2-6 works).
To answer your question, Skull_Boy: I get my inspiration from whatever comes into my mind. My maps seem to plan out as they go, straying from the original idea completely sometimes, though I find looking at reference pictures from Google Images can be very helpful.
Screenshots of what it currently looks like:
Edit: If only I could get those damn pylons to light properly. They're weird models, that's for sure.