There isn't an add a building tutorial, but it's fairly easy. You need to make the door a separate model, with the animations, add that as a separate draw model, calling the states Door_1, and such, and add a production update, with the number of doors. Look at the existing USA Airfield for more hints.
Maybe somewhere to start would be to get that propaganda door working.
Which was originally and still may be intended for the China POW Truck to transfer the prisoners inside. That would feed China an opposite of that generals power. (forgot what its called, the one where all the units are like on steroids, lol).
And then China can demoralize all the enemy troops.
Ah crap, I just gave away my idea for a mod...
Forget what I just said.
You are getting sleepy, very sleepy............<thud>