Architecture in level design?

You don't have to be an architect, think about if you had to build it, how would it all fit together. You don't even have to do this most of the time, it only matters a bit for the areas you actual go inside, but for most games you won't enter every room of every building, that's why you get away with illusions. It's never easy to make interiors and exteriors match perfectly, and many games don't even try, you load inside where the interior is twice as big as it should be (rpgs) and nobody blinks an eyelid that you've actually gone inside a Tardis. Or walls are 1 meter thick because you didn't care enough to solve for it.

If you really want to pick up the basics, just watch some documentaries on building structures, you'll find out pretty quickly how the various types of common building are constructed. Now, if you're trying to be absolutely accurate and realistic, you'll just have to do your research of the structures of the period.

If in doubt, google answers any question. I just did a search and got tons of building plans from the period.

Wanted to say what Chris said, but I was also thinking that at the time of HL Episode 2, they were saying they did research/hired expert for exactly for this sort of thing. Things are built to work and with a logic, so only research can help.

Unfortunately I can't think of any source dedicated to this kind of thing.

I guess maybe take advantage of those who made research for you? like play/watch a playthorugh of Brothers In Arms or Medal of Honor/Call Of Duty, surely they based their stuff on some research. All of this though, after you have come up with a satisfying layout, imo.