Tier 1: Federer, Nadal, Djokovic, Zverev
Tier 4: Murray
(Reason why he is a member of Big 4, still far away though)
Tier 8: Wawrinka, Cilic, Del Potro
(Wawrinka has won 3 slams but is too inconsistent)
Rest of the players would be Tier 11 or + in my opinion.
You can even include inactive...