Hi there!
I have to model this ceiling:
The square holes are trivial, since it is a combination of insets, extrude along normals, extrude…However, I’m stuck when it comes to model the circular part.
I tried with a 8 sided cylinder, but I’m not getting the desired results. How would you approach it?
I managed to figure out a solution:
I noticed that a 64 sided cylinder would work quite well regarding the fusion with the existing mesh. The results are not perfect (the 4 points of contact mean that the outer radius is not an exact circle), but it works well enough.
When I inset the cylinder in order to make the inner radius, I applied LoopTools - Circle. That was vital to achieve a perfect inner radius.
Make the basic shape with a plane, give it thickness, and use the edge bevel.
※ The bevel modifier makes it easy to adjust the edge size. 
