To make a slanted roof of your own you'll need to use a Magic cube tool.

  1. Change its dimensions;
  2. Turn it using a round arrow icon; 
  3. Lift it on top of your house setting a Levitation parameter. 

Check out our video tutorial about creating a custom slanted roof in a macOS app. However, main controllers are the same on all apps, so you won't have any issues reproducing these steps.