Re: Tall modern skyscrapers

You will be prompted to upgrade the houses to skyscrapers as you continue to play the game. That's how your population increases. So as you build more factories and stores and make more things, you will get a bubble that will have a green checkmark that shows you it can be upgraded.

If you only have a yellow builder's hat, it means you still need an item to upgrade. It will show you what you need like wood, or plastic, etc. Hope that helps @alluryn .