Estimating the slope of a roof can be difficult. With the Carpenters Angle Cam, you can measure the angle without having to climb up on the house. If you specify the length of the baseline, you will also get the approximate height of the object (eg the house) and the length of the diagonal (eg the roof).
To get more accurate dimensions and angles: support against something when you measure, stand right in front of the object and at a proper distance. The app also allows you to take pictures so you will remember your measurements. You can flip the angle so it starts from the right side. Enter your measurements in feet, inches, meters or centimeters.
Good luck with your project!