There are 10 level when building a tower for the city. The task of first level is place 10 stairs and the next level will need to place 10+5, and so on.

You have three chances when failure in first level and chances will be auto increased when go to the next level.

When you finish all 10 level or lost all chances the stair count of the tower is the points whitch you earned.

http://appshopper.com/link/buildcity