I only get c-c for some houses and buildings.
You use them to build starcases and second and third stories in your houses. You need to finish the upstairs quests, first. Once you finish the first set you will see a new section in the house ( walls, floors, build rooms'ect) thta looks weird. When tapped, it will cost like 200 c-c and your house will look very tall. You can lower the price by taking away or selling eooms in the house. (I sold the master bedroom, kids' bedrooms, and the on-suite because I will move then upstairs.)
To go upstairs, tap on the stairs and make your sim go up. If you want to ACTUALLY SEE the upstairs, press the gray button that will appear in one of the corners (under the quests for me, but I'm on an iPad) and it will go the the next story.
Yay lol good luck!