It's only been about a year since Facebook moved into its headquarters into the Menlo Park offices that once housed Sun Microsystems. But the company is already planning to expand. But instead of simply building a new wing, Facebook has much bigger plans: The new addition will span the length of eight football fields, according to a Facebook blog post. And it will boast a famous architect to boot.

Sprawling the west side of the Bayfront Expressway, the building will connect to the current Willow Road campus through an underground tunnel beneath the highway. Construction of the new west campus, which renowned architect Frank Gehry has designed, will begin in early 2013, according to the post.

One of the most notable parts of the design (besides the magnitude of the building) will be the tree-lined roof-deck garden. The roof-deck garden has become a popular feature at some tech start-ups' offices: Twitter recently relocated to a San Francisco space boasting its own rooftop rest stop.

"It's an amazing part of the building," Facebook Environmental Design Manager Everett Katigbak told the Oakland Tribune of the roof plan. "It will be much more like a park than an urban garden. There will be trees and grass; there will be walking paths."

According to the Tribune, Zuckerberg has been in talks with Gehry since the company moved from Palo Alto to Menlo Park at the end of 2011. The west campus is intended to house most of the company’s 2,800 engineers in an open, office-less space with “break away” areas for meetings and small food-stocked micro-kitchens thoughout.

"The idea is to make the perfect engineering space: one giant room that fits thousands of people, all close enough to collaborate together,” Zuckerberg wrote on his Facebook wall last week. “It will be the largest open floor plan in the world, but it will also have plenty of private, quiet spaces as well."

Perhaps because of Facebook's weak stock performance, both sides have been rather quiet about the cost of the endeavor. Gehry's Walt Disney Concert Hall in Los Angeles--a much smaller project--cost $274 million to construct. His other accomplishments include the Guggenheim Museum in Spain and The Experience Music Project in Seattle.

“The costs of the campus will be considerably lower than most of Frank's previous work,” Facebook spokesman Slater Tow told the Huffington Post. “This is especially true as the building is designed to be simple--almost like a giant warehouse, rather than a monument to Frank or Mark. Its emphasis is on functionality, rather than extravagance."

A park on a roof and on-demand food service, apparently, don't fall in the extravagant category.