Have you tried "bulldozing" your existing building and then replacing it with a new "Residential Zone"? Choose a building that has a high property value - press the residential icon and the buttons below it - you will see a Simolean and a hard hat...if the property value is high, bulldoze it and then replace it with a new residential zone (or Tokyo Town Zone) and rebuild. It will auto-magically become a glass skyscraper. Please note, it is more difficult to build the skyscrapers than the brick buildings...but it's worth it!
