"Making the sculpture has been a highly rewarding experience, " said Mr Stewart, one of four Scottish silversmiths invited to submit a design last winter.

BBC: Silversmith Graham Stewart with his work

"It's exactly like making a toy or a sculpture, " says Donnelly.

WSJ: Up in the Air | Making It

Mr Doubleday has made a preliminary model of how the sculpture will look, and is now making a clay model using about two tonnes of clay supported by a steel structure.

BBC: WWI hero Herbert Columbine honoured with bronze statue

The tower stands 114.5 meters (375 feet) tall, making it Britain's biggest sculpture, more than twice the height of Nelson's Column, almost six times the height of the Angel of the North, and 22 meters taller than the Statue of Liberty.

CNN: Orbit tower: Olympic Park's red 'roller coaster'

Viewer Jean Hobbs suggested turning a Mini Clubman car, which has been uncovered 30 years after being left in a tunnel under the Longbridge factory where it was built, into a sculpture to show off the city's car-making history.

BBC: Statue campaign 'to define Birmingham'