Apple's multi-billion-dollar Campus 2 headquarters is taking shape, as over half of its circular main building reaches maximum five-floor height. A video recorded by a drone flying over the 150-acre building site shows how the basic structures of five of the building's nine segments are complete.

Doughnut-shaped and nicknamed The Spaceship, construction of Campus 2 began two years ago and is expected to cost over $5bn (£3.2bn). Apple plans to begin moving staff in by the end of 2016. A perfect circle, the main building will cover 2.8 million square feet and accommodate 12,000 employees; it will be surrounded by parkland and reclaimed trees to help camouflage the glass building into the landscape.

The speed of the construction is in part thanks to an innovative construction method where interlocking concrete slabs are stacked on top of each other. These slabs "serve as both the ceiling of one floor and support for the raised surface of the floor above," Apple has previously stated.

Each of the building's nine segments is joined to its neighbours by hallways on four of the five floors; each hallway also stretches to the centre of the circle, where there will be a staff canteen with open courtyard.

Four months before his death in late 2011, Jobs told the Cupertino City Council that "the overall feeling of the place is going to be a zillion times better than it is now". Campus 2 has a goal of being a "net-zero energy" site, meaning it will be self-sufficient and only require power from the national grid in emergencies.

Apple Campus 2
A video from March 2015 shows how much Campus 2 construction has progressed in six months Apple Insider

To achieve this, the circular roof will be covered in 70,000 sq ft of solar panels generating enough energy to power 4,000 homes. Campus 2 is being designed by Foster + Partners, headed by renowned British architect Sir Norman Foster, who is also responsible for Wembley Stadium, London City Hall and 30 St Mary Axe, commonly known as The Gherkin.

Originally set to cost under $3bn, Campus 2's budget was increased by $2bn in 2013, before construction on the former HP site has even started.