I tend to do a grid of levels, I would hope that everyone on TF will know what that is, whether the grid is done by laser or dumpy, or both. Find the highest point, and go from there.
I have posted a few pics of the way I do this, it has nothing to do with spiked rollers, or guess work, it has to do with skill and experience.
Just for the record, laying self leveling compound, and laying sand and cement screeding are a million miles apart.
Slc is easy compared to real s&c screeding.
The void between the two will never be bridged as a bathroom tiler will never be a real tiler imo, an all round tiler will be comfortable doing the same as tiling a domestic bathroom/kitchen/ conservatory, as tiling a swimming pool,or a 10.000m2 floor.
I am a bathroom basher, but I like many other members of TF can handle anything tiling can throw at me. I hope I don't upset anyone with my candour, but I think you all know my views on this subject.