http://www.nevadaappeal.com/news/17354117-113/tesla-still-may-double-plant-size-of-gigafactory According to Hill, Tesla CEO Elon Musk said during a conference call in May that the company is considering increasing the gigafactory’s size by 50 to 100 percent but there’s been no formal commitment to that expansion yet.
WSJ report quotes Tesla as saying that 110 acres will be for "industrial purposes" and that 1836 acres will be buffer land on which Tesla would not build structures but could place solar arrays to provide power to the plant.