Path of the Titan

Some Barbarians draw power from their ancestry. Those who walk the Path of the Titan are able to fuel their rage with the giant blood that flows through their veins.
While some  warriors are direct descendants of giants, some are unaware of their heritage until it manifests with their rage. Usually tall or strong for their race, mortals with giant blood in their veins are fairly obvious once you know what to look for.

Restriction: Powerful Build Only

 Only creatures with the Powerful Build trait can choose the Path of the Titan.  Your DM can lift this restriction to better suit the campaign. The restriction reflects the inherent strength those creatures normally have, though anyone of tremendous strength could take this Path. (If you were to ignore the Powerful Only restriction consider ruling only if the character has a 16 or higher in their Strength score could they take this Path, at least in the case of multiclassing if anything)

Giant Heritage

When you adopt this Primal Path at 3rd level, the power of your giant ancestors manifests when you rage. When you enter a rage, you can chose to grow by one size category; for example, from Medium to Large. Your physical size doubles in all dimensions, and your weight is multiplies by eight. Your carrying capacity increases accordingly.

While raging, your weapon attacks deal bonus damage depending on your current size category' Medium (1d4), Large (1d12), Huge (2d12), Gargantuan (3d12)

Your Maximum ability score for both Strength and Constitution increases by 2 to a maximum of 22.

 

Giant's Blood

When you choose this path at 3rd level, you choose a type of Giant whose favor you have gained through your previous deeds. (Alternatively it could be the giant blood in your veins.)
The Giant's favor grants you a specific blessing in a keeping with their abilities.

- Fire. While raging, you gain Fire Resistance and your Rage damage is Fire damage
- Frost. While raging, you gain Cold Resistance and your Rage damage is Cold damage
- Storm. While raging, you gain Lightning or Resistance, your Rage damage is now Lightning damage.
- Cloud. While raging, you gain Thunder Resistance, your Rage damage is now Thunder damage.

Cloud Giant

You have the blood of a Cloud Giant within you.
While raging you gain Thunder Resistance and your Rage damage changes to Thunder damage.

Fire Giant

You have the blood of a Fire Giant within you.
While Raging you gain Fire Resistance and your Rage damage changes to Fire damage.

Frost Giant

You have the blood of a Frost Giant within you.
While raging you gain Frost Resistance and your Rage damage changes to Cold damage.

Storm Giant

You have the blood of a Storm Giant within you.
While raging you gain Lightning Resistance and your Rage damage changes to Lightning damage.

Titan's Vitality

Your rage draws out increasing amount's of resilience from your Giant's blood.

When you enter a rage, you gain Temporary Hit Points equal to your Class level + Constitution Modifier.
You also may increase your AC by +1 for the duration of your Rage.

Titanic Blows

Through training and experience you are now comfortable and capable with your giant size. 
All your attack's while enlarged now have the siege property, and deal 1d6 bludgeoning damage against creatures with the construct type.
While raging, your attacks now deal an extra 1d4 extra bludgeoning damage and knock creatures up to 1 size category above yours back 5 feet.

Wrath of the Titan

Starting at 14th level Once/per Short Rest you can strike with the ferocity of a full blooded giant. When you take the Attack action while raging, you can focus all your power into one devastating strike. Once per turn you may maximize all damage die rolled on a single attack.

This changes to Twice/per short rest at Level 18