No Enclave facilities were built specifically for them besides the Oil Rig, they were just VIP shelters/bases that the Enclave knew of and took over.
Equally, while the Big Empty isn't a government bunker, it is an advanced government facility and as such one would expect it to share the same interior layout and aesthetics of other advanced government facilities. These are military installations, I don't expect that there would be a lot of variance in the way they're built.
Actually Raven Rock and Hidden Valley were built by the government for the government. The enclave eixsted before the great war and built these places to hide government officials they deemed worthy.
Also just becuase the Big Empty did work for the government doesn't mean they were owned by the government. Aperture Science of Portal fame, and Black Mesa of Half Life fame were both massive research facility whose size could classify them as a city and they were privately owned corporations. The presence of Repconn, RobCo, and H&H Tool company, among possible others, I wouldn't be surprised if we found General Atomic and Poseidon energy stuff there also, show that Big empty was probably like Black Mesa or Aperture. It was a privately owned research facility that did work for the government, and since it wasn't owned by the government it doesn't need to look like pre-war government instillation.