Elon Musk’s Tesla has signaled it wants to build more near its huge factory in eastern Travis County, filing a site plan in early July for “industrial use facilities with associated improvements.” With the car manufacturer still not commenting on its development plans, these kinds of public filings offer the clearest picture of what’s going down at the gigantic site. Musk’s companies own more than 2,500 acres — that’s more than five times the size of the University of Texas at Austin campus.