After about a week of playing around with Hammer, I've come up with this map, as my first real attempt at a map.
The map is identical on both sides (except reversed). The teams start out on the main floor, with adjoining rooms that include and armory and a hallway (complete with secret passage), also includes monitors that show underground. The next floor up has a windowed room, access to the roof via two different ladders, a bridge connecting the sides of the map, and another secret room. The roof has a sniper tower. There is a tunnel system that connects the two sides.