Depends on the gpu.
If the gpu in question isn't big on power - or even a moderately hungry one - you can get away with a 240mm as top exhaust.
If it's neither, you'd best mount that radiator in the front. I'd suggest either 240/280, as they should give you enough room to mount with the tubes down.
360mm is a bit problematic:
https://www.gamersnexus.net/hwreviews/3602-lian-li-lancool-ii-mesh-case-review
"We don’t recommend mounting radiators larger than 280mm in this case: the front just barely has space for a 360mm rad, and probably only with the tubes up, which is inadvisable since it creates pump whine and water starvation after permeation sets in. The drive cage is repositionable and removable, but there’s already limited...