Captain Murphy writes...
"Bring on the cookies. 3011 San Jacinto ! Storage Bldg. Added 2 floors to the top. We can smell the cookies from here."
Good guess, but no. Remember the clue: "a building inside a building--i.e. an old building contained within a new building that was built around it."
That means, a pre-existing building completely contained by another building that was constructed on top of it and around it.
Big hint. You can see the building in this photo: