(We assume you meant 3,000,000 sq. ft. as round-off size
for the Apple headquarters footprint.)
For your edification, just go over to NASA Ames Research Center
next door, which is about that size for its extant buildings.
Now Google HQ adds 1.0-1.2 mega square feet to that, and although
re-zoning within the ARC master plan makes their original 2.5-3M sq. ft.
variable you might enjoy an R&D sandbox like that to play in!
P.S. When I interviewed with...