Wall Street Journal picked up on Tesla having bought considerably more land in Nevada this spring.
What I found most relevant from the article:
"The majority of the land—1,863 acres—is buffer land, on which Tesla won’t build structures but could place solar arrays to provide power to the plant, a spokeswoman said. The remaining 110 acres is for industrial purposes, though Tesla says it hasn’t planned to expand beyond its original footprint yet.",
"The nearly 3,000-acre site takes up about 2% of Storey County’s land area and dwarfs most factory locations. The Tesla spokeswoman says the company has options to purchase several thousand more acres as well."
and,
"The battery factory will begin producing cells at the end of 2016"
The WSJ has quite a track record of making misleading statements regarding Tesla, so I think it's worth considering the possibility that the "buffer land" statement is not accurate. As to the GF producing cells in by the end of 2016... I'm wondering if it is already understood that they will be making cells at the GF about 6 months before they produce battery packs.
http://www.wsj.com/articles/teslas-land-holdings-in-nevada-nearly-triples-1436908368
you should be able to google the title of the article and access it for free.