Maximum Champion Growth size

Solution 1:

Currently the largest possible Cho'Gath is with the Loch Ness skin, Greater Relic, Surge, Wild Growth, and 6 stacks of feast. You can see a video of it here:

More then likely more ways of increasing Champion size will be released in the future.

Solution 2:

Wingmind has a good answer ( https://gaming.stackexchange.com/a/56985/22102 ) but I do have a couple of pictures from a match me and a friend did to test this idea out I figured you would appreciate. We had only regular cho with 6x feast stacks, surge, and wild growth on summoners rift. Had a Morgana with us in our match though :)

Bigger than baron!

massive Morgana black sheild

Solution 3:

In season 6 I believe zac has a larger maximum size, in fact I believe he has since elixir of iron. Due to his passive making him larger with more hp, the largest you can make him would be cinderhulk enchant on jungle item with 4 warmogs, a steraks gage and elixir of iron. Lulu's ult makes him grow more than cho gath due to the extra health. I'm not sure how big exactly, or if there's a size limit, but if you can get steraks gage off while still at full health on him, I know you'll be much bigger than baron.