Getting My Hands Dirty With Single-Player Maps

Ok so I've been bouncing around on ideas for a map and decided to work on a single-player map, it's very small, and will only have ten or so enemies. As of now I'm almost done with creating the basics and I've started texturing the map. Here are two images:
this is the main area(I said it was small)-

href="http://photobucket.com/albums/a212/spacew00t/?action=view¤t=CombineWarehouse.jpg">Area1

And this is a cool shaft in the ground-

href="http://photobucket.com/albums/a212/spacew00t/?action=view¤t=CombineWarehousePIPES.jpg
">Shaft