Fairly basic, but after chris0312s appraisal of emp_2fort [which was fair] I've decided to practice my brushwork and make something half decent. I've made a bunker capable of holding about 2 tanks maximum with high defensive capability, with or without infantry. It sports a pair of doors which infantry can shoot happily from, and tanks can fire over, but they can be lowered into the floor if the tank wishes to leave. I'll probably add a constructable piece by the door [think NS] to allow you to open it. But now I'm rambling. How's it look? Textures aren't done fully yet, but that's probably how it's gunna look. I'm quite happy with it. Funnily enough, this was the reference It will be used in a large flags map involving tanks, possibly more than once.
My main issue with it is that the roof looks like it's not really attached properly. I guess this is because it lifts off in your reference or something but it's not something you'd want in a bunker. Make it thicker, and make it look like it's the same block of concrete as the walls, alternatively you could simply attach it more firmly by putting blocks of concrete connecting it to the walls. Also I'm not sure how it's supposed to work.
There's a door at front and back, I agree, the roof is ugly. I'm working on fixing it. And yes mayama, there will be more textures. At the moment I'm just trying to get the doors working.
Oh brother... i"ll wrap up smething in hammer for you guys i guess it cant be helped edit: total flexibility can be achieved with a funk_tracktrain