Construction on what may just be the world's next tallest building is (finally) due to begin, Lloyd Alter of Treehugger reports.

Broad Sustainable Construction told Atler that the construction of Sky City would begin in June, after a lengthy delay due to a "long and arduous approval process".

When complete, Sky City should be the tallest building in the world at 838 meters — 10 meters higher than the Burj Khalifa.

The building, being built in an empty field near the city of Changsha, is being billed as the future of sustainable urbanization, a city-in-a-skyscraper that will eventually house 30,000 people.

This promotional video gives you a sense of what BSC is aiming for:

It's pretty awe-inspiring, but we haven't even got to the perhaps the most audacious part yet. When BSC announced the building, they said that they would complete the building in just 90-days.

While they now appear to have pushed that timeframe up to seven months, that's still not much time at all — for example, the Burj took five years to build.

The company also says that the cost of the construction will be $628 million; in comparison the Burj cost an estimated $1.5 billion.

Is that even possible? Last year Christian Sottile, the Dean of the School of Building Arts at the Savannah College of Art and Design, told Business Insider that though the concept might work, "if you look at the outcome of this endeavor urbanistically, it is at best a folly, and at worst, madness."

BSC has a history of fast constructions, however. The group was behind a three-story building that went up in nine days and a 30-story hotel constructed in just 15 days.

Check out time lapse video of the 30-story hotel being built below: