Thunder Storm and then Energy Shield. Energy Shield is to convert certain percentage (80% would be enough) of received damage to mana rather than life.
Remarks:
Nova makes a considerably large area damage, but requires the sorceress to be close to the targets during conflicts.
Static Field has very high level for this build. Plus the lightning sundering and high reduction on enemies’ lightning resistance, the sorcress can often reduce the life of enemies in a large range to (often less than) half with a few casts of Static Field.
This sorceress build has many surplus skill points since Nova has Static Field as the only synergy skill. Hence it is wise to invest the remaining skill points to Energy Shield. In addition, an Act II mercenary with Meditation Aura (by wielding a weapon with Insight runeword) to quickly regenerate mana.
Investing all stat points to Energy can put maximum mana on sorceress, and her mana regeneration will consequently be very fast (the base regeneration rate is to recover full mana in 2 minutes, no matter what the maximum mana is, and faster regeneration increase the rate by the specified percentage). However, with maximum mana more than maximum life, the sorceress may suffer the curse of Blood Mana from Succubi and Baal, which consumes the sorceress’ life instead of mana when she casts any spell. A means to avoid this is to invest both Vitality and Energy, such that life is a little more than mana with all gears/charms on. Another advantage of doing so is that Energy Shield can only reduce damage by 25%: With purely invested 20 points on Telekinesis, 1 point of damage consumed by Energy Shield only costs 0.75 mana. However, it does not benefit from any resistance of the sorceress. More life also helps to avoid sudden death when the Energy Shield is off.
With Energy Shield on, only about 20% recieved damage goes to life. Therefore, a Skin of the Vipermagi with higher damage reduction is preferred.
Thunder Storm makes periodic attacks to a single target. It can assist the sorceress in real battles.
Gears
Weapon: Two-hand weapon with low strength requirement (such as Scythe) with Infinity runeword for its –55% Enemy Lightning Resistance and level 12 Conviction Aura (-85% Enemy Light/Fire/Cold Resistance, -17% for immune enemies).
Helm: Griffon’s Eye for its +1 All Skills, +25% Faster Cast Rate, and –20% Enemy Lightning Resistance. Socket a lightning facet for an additional –5% Enemy Lightning Resistance.
Gloves: Magefist for its +1 Fire Skills (one Warmth skill slightly helps the regeneration of mana) and +20% Faster Cast Rate.
Belt: Arachnid Mesh for +1 All Skills and +20% Faster Cast Rate.
Armor: Skin of the Vipermagi for +1 All Skills, +30% Faster Cast Rates, +35 All Resistance. Better with -13 received damage as the build uses energy shield and only a small percentage (usually less than 20%) of damage goes to life, which makes the reduced damage attribute useful. Add one socket with one Lightning Facet for -5% Enemy Light Resistance. This armor should not be upgraded or it requires lots of strength.
Rings: Stone of Jordan on both hands, each providing +1 All Skills, 20 mana, and +25% Maximum Mana.
Boots: Rare Boots with Lightning, Fire, and Poison Resistances. Additional +30% Faster Run/Walk Speed and +10% Faster Hit Recovery are also beneficial. Poison Length Reduction and Half Freeze Duration are also useful attributes.
Amulet: Caster amulet with +2 Sorceress Skills, +10% Faster Cast Rate, some resistance on Lightning (more important than other elements), Fire, and Poison. Strength and life are also useful attributes.
Switch Weapon and Shield: Crystal Sword or Flail with Calls to Arms runeword to bump all skills by 1 and life/mana for 60%+, and Monarch shield with Spirit runeword to increase the skill levels on Call of the Arm.
Inventory: Sorceress Torch, Annihilus, Crack of the Heaven grand charm (the Lightning Sunder grand charm), 7 Lightning Skill grand charms with life or Faster Hit Recovery, All Resistance small charms with life or Faster Hit Recovery to make 43% Faster Hit Recovery, and max out Fire/Lightning/Poison resistances, and more life the better.
Remarks
+19 lightning skills: 1 from helm, 2 from amulet, 1 from armor, 1 from belt, 2 from rings, 3 from Torch, 1 from Annihilus, 7 from skill grand charms, and 1 from Battle Command on Call to Arms.
-85% enemy lightning resistance: -25% from helm, -55% from weapon, and -5% from armor.
+105% faster cast rate: +25% from helm, +10% from amulet, +30% from armor, +20% from belt, and +20% from gloves.
Mercenary
Use Act II Mercenary with Prayer Aura and the following gears:
Weapon: Ethereal Thresher/Giant Thresher/Great Poleaxe with Insight runeword for its Meditation Aura.
Helm: Ethereal helm with high defense and the Cure runeword for its level 1 Cleansing Aura to reduce poison length and curse duration.
Armor: Ethereal armor with high defense with the Chains of Honor ruenword for boosting all resistance and life leech.
Remark: The combination of Andariel’s Visage and Fortitude runeword can be an alternative for high defense at the cost of losing the Cleansing Aura.
Summary
Attack: Cast Static Field 2 to 3 times and then Nova to clear out. Keep Thunderstorm on to help the killing. This build has -85% enemy lightning resistance and needs +105% Faster Cast Rate.
Survivability: The Fire, Light, and Poison resistances should be maxed out to 75%. The Cold resistance is at a high level over 30%. energy shields absorbs 80%+ of received damage.
Supply: Mana can be regenerated quickly with the Meditation Aura. The life can be slowly regenerated by the combination of Prayer Aura, Meditation Aura and Cleansing Aura from the mercenary.