Determine Your Roof Pitch
You might need a ladder for this. There’s two ways to determine what the pitch (or slope) of your roof is, neither of which is very complicated.
You can figure out your roof pitch by taking a level and marking from the left side of it, a mark 12” over to the right. Next, and from up on your roof, you’ll hold the level straight and level (bubble centered) and then measure the vertical distance down from the bottom right end of your 12” mark on the level down to the roof.
This is the amount your roof inclines in a 1-foot span or the “pitch” of your roof.
Or, if your roof has tile or some other type of irregular material,
you can go up in the attic and do it like this: