What is the history of the "Superbay" at San Fransisco International?
Superbay Hangar is a maintenance facility at San Francisco Airport.

About previous tenants and when it was built, this forum mentions that:


  It is the large aircraft hangar built by AA in the 1970's to house the
  747. Both AA and TWA were the first tenants. Now it's UAL and AA. UAL uses it as a line maintenance hangar for the wide-body fleet.
  
  It sits all alone out towards the bay. When VIP's come to SFO, they
  park next to this hangar due to its isolated location.
  ...
  The SuperBay was built and is owned by the City of San Francisco. It
  is primarily used by UA/AA.


Going through the timeline on SFO's History, the vacant area of this hangar is visible in one of the pictures of 1960s. In later pictures (1981), it appears to be there (shown in the background)1.

Interestingly, more references are found about this hangar in the future development plans of the airport than the history. Examples can be seen here (PDF, p20 and 28) and here (PDF, p6). This site also talks about some future work for Superbay Hangar.



1: I am not 100% sure about direction of the camera, but it might be pointing towards that hangar.