If we assume the giant anatomy compensates for their greater weight, so that their strength increases faster than simple geometry suggests, which is plausible, the weight of armor they can carry could scale with their weight, they would be able to carry thicker armor. Unfortunately, the reason this is plausible is because the required increase in strength is small enough. Thus the increase in armor strength is also not that dramatic.
Considering chain mail, the larger giants could have the same level of comfort from chain mail with proportionally larger links. This would make the armor more rigid and better able to distribute the energy of attacks. Combined with the assumed increase in thickness, giant chain mails should be noticeably better than normal human chain mails. Additionally since this scaling would keep the total number of links the same, the giant chain mail should not be dramatically more expensive.
In contrast a plate mail would be slightly less rigid than the scaling would suggest and the amount of work would scale more linearly. So chain mail is a fairly good choice for giant armor.
Unfortunately, what chain mail is not, is a good material for cloaks. Cloaks need a light and flexible material to flow properly to be comfortable and retain mobility, chain mail is neither. Also chain mail assumes having padding inside to absorb the energy of blows; the chain just stops the weapon from penetrating and spreads the impact. Essentially it makes edged weapons and large enough pointed weapons work like blunt weapons, the padding actually absorbs the impact. The padding also protects the user from chafing and, in case of a cloak, impacts caused by the armor.
So, no to chain mail cloaks. The giants would use normal cloth for cloaks. That said, cloaks actually were used defensively in melee combat, to confuse and entangle opponents. The giants totally would use their giant cloaks against any normal size opponents. If made from cloth resistant to tearing the cloak would entangle pointed weapons penetrating it. This might actually be important if you are wearing a chain mail the point might otherwise slip thru.