Need App to measure slope of a surface

[koam]

I'd like to find an app that will measure the slope of a surface that the phone is placed on.

For example, you run the app, put the phone flat on a roof and have it measure the slope of the roof or the angle of the roof, such as 40, 45, or 50 degrees.

I see a bunch of level apps. If anyone knows of one that works well, please let me know.

Thanks