Now here's something interesting. Here's Tesla's Gigafactory and nearby buildings in Google Earth.[1] There are three buildings about 3000 feet northwest of Tesla's that are about the same size as Tesla's building. There's another big one about 400 feet to the west. What are they? This is an industrial park zoned for Really Big Rectangular Buildings, the Reno-Tahoe Industrial Park.
The building to the west is PetSmart's distribution center. It's almost as big as Tesla's building. Just to the west of it is a WalMart distribution center. That's two buildings, but they add up to about the size of Tesla's.
The identically-sized buildings to the northwest are the Eagle Valley Industrial Center.[2] CBRE seems to be building two rows of 500,000 square foot buildings and leasing them to companies that need distribution centers. They have Amazon, Diapers.com (owned by Amazon), chewey.com (not owned by Amazon), and other tenants in the third building. Markings on the ground indicate that buildings #4 and #5 are coming along soon. The distribution centers aren't built as big single buildings because they need lots of outer wall for loading docks. Zoom in and you can see that semitrailers are docked along most of the east and west exterior walls. That's a distribution center - stuff comes in one side, and goes out the other.
So, while Tesla does have the biggest single building in that industrial park, CBRE has more floor space than they do.
[1] https://goo.gl/maps/4rWXYqxa1Eo
[2] http://ktrcapital.com/PDF/Brochure/NV%20-%20Eagle%20Valley%2...