Roofing takeoff for Fire rated decking

I need to measure fire rated decking for roofs. Fie rated decking starts at the eave of a roof (yellow line) and only goes up 5' in the direction of the green arrow. The issue I have is that the software isn't letting me change where the slope (run) starts. It defaults to the green arrow being where the eave starts and the rise being in the direction of the red arrow. I need to reverse this. any suggestions?