Well... really, first I'd find a mini that works as both a goliath and a mage, determining their weapon. Likely customising. (Getting some other weapon proficiency would be nice, but really I'd just try and find a neat quarterstaff.)
Instead of a spellbook, I'd have the character use runic tribal tattoos. As they learned new spells, they'd etch them on their flesh.
An acolyte background would work to, reflavoured as more spiritual and less clerical. Give them a history with shamanistic practices that blend the arcane and the divine. Play them as touched by spirits and possessing otherworldly lore, talking enigmatically with lots of non sequiturs.
