Goliaths have Powerful Build racial trait. It allows, among other things, "use weapons designed for a creature one size larger without penalty". So, as I understand, goliath character may fight with large greatsword using 2 hands. What about using medium greatsword with 1 hand? Is it possible? Is there -2 penalty as for large creature using medium weapon?
First of all, why wouldn't the goliath use a large-size longsword? It has the same damage as a medium-size greatsword.
Anyway, let's look at the rules:
Inappropriately Sized Weapons
A creature can’t make optimum use of a weapon that isn’t properly sized for it. A cumulative -2 penalty applies on attack rolls for each size category of difference between the size of its intended wielder and the size of its actual wielder. If the creature isn’t proficient with the weapon a -4 nonproficiency penalty also applies.
The measure of how much effort it takes to use a weapon (whether the weapon is designated as a light, one-handed, or two-handed weapon for a particular wielder) is altered by one step for each size category of difference between the wielder’s size and the size of the creature for which the weapon was designed. If a weapon’s designation would be changed to something other than light, one-handed, or two-handed by this alteration, the creature can’t wield the weapon at all.
And the goliath:
A goliath can use weapons designed for a creature one size larger without penalty. However, his space and reach remain those of a creature of his actual size. The benefits of this racial trait stack with the effects of powers, abilities, and spells that change the subject's size category.
It's pretty clear that a goliath is a medium creature who can use large-size weapons (without penalty). This implies they can also use medium-size weapons (being medium-sized creatures).
The question here is, however, can he use medium-size weapons as a large creature. The answer is no, because:
- A goliath is a medium creature
- Using a medium-size greatsword requires two hands for medium creatures
- Nothing about a goliath contradicts the above two rules