Who are the biggest champions?

So, I was thinking about this the other day when I rewatched New Dawn and saw Nautilus; I was just wondering how big some champions are and who exactly are the biggest? Here's who I've got: Has the potential to be the biggest of all the champions once he has consumed enough. I sort of don't want to count him since his starting size isn't as big. This guy is massive! Before New Dawn I had thought he was only slightly larger than the average person. The mine cart in his splash art and the soldiers in his reveal art give us some idea as to his scale. He's not so much tall as he is wide. I'm really getting vibes of scorponok from Bayformers (in a good way, that was one of the few good parts from the film) Does anyone have any idea as to how big Maokai is? I'm just sort of assuming he's a little shorter or the same size as Nautilus. The person in Malphite's splash art shows us that this guy is very big as well.

Then there is the enigma of Rek'Sai. I really haven't gotten a good sense of scale from her. Right now I'm assuming she is slightly smaller than Skarner