Here's my build:
5 piece Kags (chest & legs infused tri-stat, belt & gloves nirnhoned mag, boots reinforced mag), 2 piece Engine Guardian (head infused tri-stat, shoulder divines), 3 piece Willpower jewelry (2 healthy 1 arcane, all spell damage enchanted), 2 piece Hist Bark 1h/s (for the physical resist, as I'm Breton) on both bars. I use tri-stat food and tri-pots.
The main skills to concentrate on are, in order of importance, as follows:
0: Bolstering Darkness this shit is OP af.
1: Taunt - This part is obvious, you need to taunt the mobs. I use Inner Rage, as NB lacks the chains of DK for mob re-positioning and pulling mobs that spawn in fights where you don't want the boss to move (like Serpent in SO).
2: Major & Minor Resolve/Ward - As a mag NB, you get the major ones from Shadow Barrier for 11 seconds when you cast Refreshing Path, and the minor ones from Mirage. Mirage also gives you Major Evasion, which is huge, and most other mag tanks don't have access to without burning fuckloads of stam/using Hist Bark 5-piece.
3: Stat sustain - Siphoning Attacks + proper weaving, no more to say honestly.
4: HP Sustain - Refreshing Path and Swallow Soul are the main HOTs you use. Refreshing Path also gives you your resist buffs, so is absolutely invaluable. In big mob pulls, spam Sap Essence to heal yourself + everyone around you to full every time you cast.
5: Damage - As a NB tank, you can actually do (a little) damage, and your HOTs rely on your spell damage and max magicka. Structured Entropy is a must, the passive HP and active Major Sorcery + heal is too good. Inner Light is also vital. I light attack weave Swallow Soul whenever I'm not buffing myself, generally getting around 8k DPS. Impale is also nice to have on your back bar.
Your bar setup is up to you, just remember that you want Entropy+Inner Light on your front bar for their passives + the Mages Guild passives.
Pic related is my stats when buffed (without undaunted passive atm though).
