JEDDAH, Saudi Arabia (CBS) — Two Chicago architects are in Jeddah, Saudi Arabia Tuesday, unveiling plans for what would be the world’s tallest building.

WBBM Newsradio 780′s Regine Schlesinger reports construction of the $1.2 billion Kingdom Tower is due to take 5 1/2 years.

LISTEN: Newsradio 780′s Regine Schlesinger reports

The Chicago-based architecture firm of Adrian Smith + Gordon Gill won a worldwide competition to design the 163-story Kingdom Tower.

Speaking from Jeddah, architect Gordon Gill says it will be twice the height of Chicago’s Willis Tower.

“You might think of Willis and Willis, stacked one on top of each other,” he said.

Is there any limit to how tall a building can possibly be built?

“There are some limits in terms of elevatoring and the cable for the elevators that are currently on the market today – about 550 to 600 meters, so we introduced the idea of sky lobbies to transfer people from one set of elevators to another,” he said.

Gill says the with the Saudi Royal Family bankrolling the project, he’s confident Kingdom Tower will be completed and become the world’s tallest building, at a height of more than 500 feet taller than the current record holder, the Burj Khalifa in Dubai.

Adrian Smith was also the chief architect for the Burj Khalifa, which was designed by Chicago-based Skidmore, Owings and Merrill.

From its completion in 1973 through 1996, the Willis Tower – then known as the Sears Tower – was the tallest building in the world. It maintained the record for the building with the most floors until the Burj Khalifa surpassed it.

The Burj Khalifa is also now not only the world’s tallest building, but the tallest structure ever built.

So far, attempts to win back the tallest building for Chicago have not worked out. The Chicago Spire would have risen 2,000 feet – only behind the Burj Dubai – but the soaring design by architect Santiago Calatrava never amounted to more than a foundation hole as financial problems dogged its developers.

Back when the Sears Tower was still the world’s tallest, the Miglin-Beitler Skyneedle stood to rise 550 feet above it from the corner of Madison and Wells streets. But the recession of the early 1990s put an end to those plans.

And back in 1956, when New York’s Empire State Building was still the world’s tallest, Frank Lloyd Wright unveiled a design for the Mile High Illinois. It would have risen exactly one mile into the sky, taller than any building now standing or the planned Kingdom Tower. But the Mile High only ever existed as a design.