It is amazing how fast you can go from photo to awesome in-game environment using SketchUp and the source Hammer editor.
I am making this game map in modular chunks, finishing one section at a time. This should reduce compile times for each chunk and speed the overall project along.
Just six hours ago the "ThunderCloud subs" location below was just a reference photo. Now it is a creepy zombie hangout.
Note: the signs and textures are not yet final.