I've made homebrew suggestions, before, on how to pull off a truly oversized weapon build before, but obviously those would not be official to any degree.
In the official rules, though, wielding anything that is actually bigger than you're supposed to wield is a near-no, and was only relatively recently changed from "you can't do it at all", to "you can go with something that is effectively one step bigger than it should be."
If you're in a home game, and want a set of guidelines that should make it possible to wield oversize weapons without going too far out of balance, I've linked to my earlier thread
There'd still be a practical limit, and definitely wouldn't work for organized play. However, in a home setting this might work well enough as a houserule if you're set on the trope of huge-weapon wielding characters.