Keep in mind that your allied contingent technically has to be its own mini-army following many of the usual rules for list creations, meaning the Giant is only unlocked at a 3200pts Chaos Dwarf army.
You can find a unit-by-unit breakdown for allies and mercenaries in the Big Chaos Dwarf Tactics Compendium
Of note, Val’s Renegade Army List pack has the Giant included in the army list, you’re probably better off just using that army list. Discuss with your opponent first, though.