Those are the backlots of the studios (though there are fewer than there used to be these days). For most of these, the architecture is pretty minimal and they are just facades that get dressed up to be one thing or another. A few are actually used as studio offices. Pay close attention and you can start to ID them pretty easily. Indoor sets are a different beast. They are built on sound stages and while an ongoing production will have it's handful of standard sets, they are struck when the production ends and the studios don't tend to keep an inventory of commonly needed interiors (eg: every Oval Office you see has been built for that production). ETA: Here is a little article about some of the Oval Office sets. One popular one owned by Warner Bros. gets broken down, stored, then rented out and set up again repeatedly for filming.