An aerial view of Facebook's new campus, an expansion of its current headquarters in Menlo Park, Calif. The LEED-certified building, known as MPK 20, has a 9-acre "green roof."

Facebook didn't hold back in its expansion of the company's Menlo Park, Calif., headquarters.

The 430,000 square ft.-building, known as MPK 20, can hold up to 2,800 people and is certified by the U.S. Green Building Council, according to sources familiar with the project. It includes a 9-acre green roof — that's roughly the size of seven football fields — with a half-mile walking loop and over 400 trees.

The building, which Facebook announced in August 2012, was designed by renowned architect Frank Gehry's firm, Gehry Partners. Though Gehry's name is tied to several elaborate landmarks including the Walt Disney Concert Hall in Los Angeles, Calif., the Canadian-American architect said the Facebook's new campus has a decidedly simpler design.

"From the start, [Facebook CEO Mark Zuckerberg] wanted a space that was unassuming, matter-of-fact and cost effective. He did not want it overly designed," Gehry said in a statement. "This is the building that we created for him."