Build:Frost Mage

Full Build Details
A few notes! :)
 * Use whatever backpack you want, the Preservation Backpack just makes me feel more mage-ish and you can keep mana/health regen-food for a long time!
 * The reason I chose Blue Chamber Collective is because you can get the Crimson Plate Set as a reward and the boots + armor gives 40+ frost damage. (Stay clear of the helmet though as it gives +20% mana cost)
 * I went for +8 mana I think when I activated it at the Leyline, I never run out of mana during fights and I have no problems with health so far, playing hardcore so I would know. ;)
 * The tank buddy aka Summoned Ghost can basically clear ghost areas on it's own, in other situations it sometimes keeps enemies from getting near your sigils so you'll have to experiment a bit.
 * If you have the DLC and you're pretty late-game, consider getting the Rust Lich Boots which gives -30 physical attack and +25 frost attack.
 * If in trouble, pop Mana Ward for 4 seconds of invulnerability.
 * Before getting the White Priest Mitre, consider using the Wide Blue Hat. ^^
 * Personally I cast all the elemental boons, wait for them to expire and cast them again, etc. You'll regain burnt mana and get +30% resist to all the elements. (because of Shamanic Resonance). Leyline Connection will regen it faster than your boons expire so it doesn't really cost you any mana. :)
 * There is another frost skill that I just now remembered, Flamethrower used on an Ice-Flame Torch, feel free to experiment!
 * If you have the DLC then Chill Hex is probably a good call, giving -25% frost resist. Cred goes to redditor Khentrok.

Best of luck! ^^