De Rotterdam is one of Koolhaas’ most inventive buildings in my opinion. It is a mixed usage skyscraper with very unique features. The tower begins connected for six floors then separates into three different towers. at about 90m above ground the towers separate in different directions. This is to enhance the wind stability of the building as well as provide space for terraces. Koolhaas went with this design choice because he knew most people would view the building from a moving car, the shape he used would cause the towers to merge and separate as one’s view changes. The building’s construction began in 2009 and was completed in 2013. It cost 340 million euros to build.