Drop Ceiling and

I'd expect they should be able to get it level and flat. Is there some extenuating circumstance the contractor cited?

Waited10years,

Skim coating ceilings on the existing slab can result in some waves but if they dropped the ceiling it should not be an issue

they did drop the ceiling and then used sheet rock. There have already been some cracks that they have repaired. Now I notice the waves even more that they Spackled the cracks. Very frustrating as this is a large job and it seems like excuses for everything that come up.

You need to tell your contractor to bring in a new plasterer. I assume there is no architect or design involved? You might want to have a painter come in and take a look at it