UK studio Foster + Partners is reportedly designing a two-kilometre-high skyscraper in Riyadh, Saudi Arabia, which if completed would be the world's tallest building.According to a report in UK architecture magazine Architects' Journal (AJ), the UK studio is designing the megatall skyscraper for a site to the north of the Saudi capital.The AJ reports that the skyscraper will be located near the city's international airport, which is currently being redeveloped by Foster + Partners.Skyscraper would be world's tallest buildingIf built, the skyscraper would become the world's tallest building, being over twice the height of the current record holder, the 828-metre-high...