Wavy roof

[Joe Funderburk, CMI]

I'd use a variation of this: "The roof sheathing appears to have a dip or sag or raised area at the *LOCATION(roof)*. We can elaborate on the possible reasons for this, but you should have a roofing contractor evaluate the roof or comment on this specific feature."

You don't have to determine the cause. Just need to describe the issue and let a roofer figure it out.