The Altoona City Council will consider a site plan for the third building at the Facebook Inc. server farm north of Interstate Highway 80 and west of Northeast 56th Street. The 632,690-square-foot structure will be the largest of the three Facebook buildings and is part of the social media company's overall $1 billion project. City Administrator Jeff Mark said construction is planned for this fall. The company, which has a total of 192 acres in Altoona, does not plan a fourth building, though the site would accommodate additional construction, Mark said.