Okay, this is an example map showing how valve did the revolving door in the first level of HL2.
One of the doors is ripped straight off the HL2 level, its an SDK example map. Another is one i made myself, and i copied exactly the properties of the HL2 one, and then i just made a glass one for fun.
Basically all you do is make the + shaped part a physbox and put a hinge in the middle.....look at the .vmf and you'll see
Nice example...Saves having to build one yourself.
Now to use it in the right levels...