Hello,
I had a new flat roof put on my addition about 4 months ago, from a roofer with a good reputation. Now, I see the flat roof material is wrinkling under the shingles. What is causing this? Can it be fixed? I just noticed this in the last month or so.

I called him and he is coming out to take a look.
Thanks

here is the other picture. You can clearly see the wrinkles.
thanks

No picture, but the wrinkles your speaking of is common on flat roll roofs. This is caused by the roofer not laying the roll material out flat and using proper nailing patterns. As time moved on the pressure from the material not laying properly has caused it to lift and buckle. While this may not cause any leaks in the near future, it will cause the roof to fail sooner then it would have if the material was indeed done right.
It should be removed and replaced. Do not accept cutting the roof and re-nailing it down.