Only using Paizo published material:
Take a look at the Titan Fighter fighter archetype. It has the ability to use oversized 2H weapons (even Titan Mauler Barbarian Archetype can't do this) with a total -4 to hit that gets reduced incrementally to -0 by 15th level.
Also consider the spell/potion Enlarge Person. Great link to explain size changes (in the sidebar).
And there's also the Impact enchantment (+2 bonus) that increases the damage 1 size larger...
Ok, so lets use a Greatsword as the example...
greatsword designed for M creature 2d6, 8 lbs., 50 gp cost.
greatsword designed for L creature 3d6, 16 lbs., 100 gp cost.
greatsword designed for H creature 4d6, 32 lbs., 200 gp cost.
greatsword designed for G creature 6d6, 64 lbs., 400 gp cost.
So you're playing a M creature, Titan Fighter and wielding a 3d6 oversized greatsword. You then Enlarge Person and you're now L, you're greatsword is now H and deals 4d6. Then you get a Large magical Greatsword +1 Impact and you're dealing Gargantuan sized greatsword damage: 6d6.
anything that increases your to hit is worthwhile. (weapon focus, etc)
vital strike for double weapon dice, improved vital strike for triple weapon dice, greater vital strike for quadruple weapon dice ("but then I only get 1 attack!" yeah, don't miss and take Power-Attack, Cleave, Cleaving Finish --> you can't vital-strike/cleave but you're probably killing whatever you hit with your big vital strike and cleaving finish works with that.
if you decide to multi-class to be self-sufficient on the Enlarge Persons, consider Vivisectionist Alchemist archetype for potions, +STR mutagen and sneak attack... also take the "Accelerated Drinker" Combat trait to be able to drink a potion as a move instead of a standard.