In an effort to attract top tech talent, Facebook is spending $1 billion to expand its Menlo Park headquarters. It just opened a new building, called MPK 21, that was designed by architect Frank Gehry and cost about $300 million. The 525,000 square-foot building will house about 3,000 employees and includes a 3.6-acre rooftop garden, a redwood forest in a courtyard and a tiered outdoor amphitheater akin to a botanical garden.

CNBC got an exclusive first look inside the new building.