...and maybe some other random builds later on.
But my two favorite schools necromancy and conjuration. And since those are fun schools here are the sorc builds that combine those two.

The first variation props up your ray attacks a bit more while the second arguably stronger one just goes for cut-throat difficulty class on stinking cloud and end game circle of death/ wail of the banshee.


-with meta magic quicken rod for level 6 spells I can instantly wipe whole encounters and screen with one cast (circle of death) - feels kinda fun but cheesy. Strong Single targets get the Enervation+Umbral Strike treatment (and scorching rays if they are still around)


Palid Raymaster


Arcane Trickster 10 / Eldritch Knight 5 / Sage Sorc 4 / Vivisectionist 1
Lawful Evil
Race: Human
7 Str / 18 Dex / 14 Con / 19 Int / 8 Wis / 7 Cha
All points into Int
Skills: Persuasion, Perception. Mobility, Trickery, Knowledge Arcana , and 2x more of your choice...stealth and knowledge world are the best choices for bonuses here.

Notable Items I like: +8 stat hat, Cloak of Sold Souls, Staff of Whispering Souls, Amulet of Four Elements, Ring of Circumstances, Greater Belt of Perfect Components, Arcane Annihilation Robes (or Leviathan's), Death from Afar Bracers (+4 ranged attacks)

Leveling:
1. Vivisectionist - all spells but you will be using true strike basically. Point Blank Shot+ Precise Shot

2. Sage Sorc - Take Grease + True Strike (or Shield first) Feat Spell Focus: Conjuration
GREASE, True Strike and Shield are the first spells we take...the rest are whatever (full spell list will be bellow leveling section)

3-5 Sage Sorc - at level 3 we take Feat: accomplished sneak-taker, @5 we take Spell:Specialization and specialize in grease or glitterdust until we get stinking cloud then we just specialize in the stinking cloud until later when we switch to circle of death

6-15 Arcane Trickster all ten levels.
Feats during these levels: 7 Weapon Focus: Ray 9: Dazzling Display 11: Metamagic Heighten Spell 13: Spell Focus Necromancy 15: Martial Weapon Proficiency
Spells to take priority per level of the spell in order:
Level 2: Glitterdust, Mirror Image, Sense Vitals, Scorching Ray (or Melf's if you want to stay more rp friendly), False Life
Level 3: Stinking Cloud (always will be specialized in and heightened later), Haste, Displacement, whatever (group buff spell like resist energy, see invis protection from arrowsetc goes here)
Level 4: Acid Pit, Greater Invis, Controlled Fireball, Enervation or Animate Dead (your choice)
Level 5: Acidic Spray, Angelic Aspect, Echolocation, Stoneskin Communal


16-20 Eldrich Knight

Feats: Eldritch Knight 1: Shatter Defenses, 17 Metamagic: Quicken 19: Greater Spellfocus: Necromancy (or improved Crit Ray) 20 (EK 5): Weapon Specialization: Ray
Spell Specialization is shifted to Circle of Death once we get that and to Wail of the Banshee or Horrid Wilting during the end levels


Spells:
Level 6: Circle of Death, Acid Fog, Greater Heroism
Level 7: Waves of Exhaustion, Umbral Strike, Firebrand
Level 8: Seamantle, Horrid Wilting/ or Dragonkind 3
Level 9: Wail of the Banshee

Has surprise aoe sneak attack on spells like CB Fireball and Circle of Death and Wail/ Wilting and pretty good ray bab thanks to 5 EK levels. Powerful spells while maintaining sneak attack damage on ray attacks and cantrips throughout the game.



Variation 2

Doctor Death
...poisonous gas, acid and death spells

Arcane Trickster 10 / Eldritch Knight 5 / Sage Sorc 4 / Vivisectionist 1
Lawful Evil
Race: Human
7 Str / 18 Dex / 14 Con / 19 Int / 8 Wis / 7 Cha
All points into Int
Skills: Persuasion, Perception. Mobility, Trickery, Knowledge Arcana , and 2x more of your choice...stealth and knowledge world are the best choices for bonuses here.

Notable Items I like: +8 stat hat, Cloak of Sold Souls, Staff of Whispering Souls, Amulet of Four Elements, Ring of Circumstances, Greater Belt of Perfect Components, Arcane Annihilation Robes (or Leviathan's), Death from Afar Bracers (+4 ranged attacks)

Leveling:
1. Vivisectionist - all spells but you will be using true strike basically. Point Blank Shot+ Precise Shot

2. Sage Sorc - Take Grease + True Strike (or Shield first) Feat Spell Focus: Conjuration
GREASE, True Strike and Shield are the first spells we take...the rest are whatever (full spell list will be bellow leveling section)

3-5 Sage Sorc - at level 3 we take Feat: accomplished sneak-taker, @5 we take Spell:Specialization and specialize in grease or glitterdust until we get stinking cloud then we just specialize in the stinking cloud until later when we switch to circle of death

6-15 Arcane Trickster all ten levels.
Feats during these levels: 7 Weapon Focus: Ray 9: Dazzling Display 11: Metamagic Heighten Spell 13: Spell Focus Necromancy 15: SHATTER DEFENSES
Spells to take priority per level of the spell in order:
Level 2: Glitterdust, Mirror Image, Sense Vitals, Scorching Ray, False Life
Level 3: Stinking Cloud (always will be specialized in and heightened later), Haste, Displacement, whatever (group buff spell like resist energy, see invis protection from arrowsetc goes here)
Level 4: Acid Pit, Greater Invis, Controlled Fireball, Enervation or Animate Dead (your choice), Dimension Door (sage sorc bloodline)
Level 5: Acidic Spray, Angelic Aspect, Echolocation, Vampiric Shadowshield

16-20 Sage Sorc*

Final Feats: Elemental Focus: Acid, Greater Spell Focus: Necromancy, Greater Elemental Focus: Acid or Metamagic: Quicken (if all the rods in the game are not enough)

Spell Specialization is shifted to Circle of Death once we get that and to Wail of the Banshee or Horrid Wilting during the end levels

Spells:
Level 6: Circle of Death, Acid Fog, Sirrico
Level 7: Waves of Exhaustion, Caustic Eruption, Umbral Strike
Level 8: Seamantle, Horrid Wilting, Dragonkind 3
Level 9: Wail of the Banshee, Fiery Body, Heroic Invocation

*at level 20 you can go into level 2 Vivisectionist to get Cognatogon Intelligence for an extra +2 DC on spells but the trade-off is STEEP for a sorc/AT: it is basically cognotagon vs 2x Level 9 spells (Fiery Body+Heroic Invocation), 1x level 8 spell (Dragonkind 3) and dimension door (level 4). The reason is we just hit level 9 sage sorc @ toon level 20 and get a bunch of free bloodline goodies right at this point.

These builds are pretty powerful and you can argue elemental damage (stormbolts) vs non-elemental (necro) damage all day - but you have to be careful with Doctor Death as several of his spells (Caustic Eruption+Wail and Circle of Death) kill everything in sight - foe and ally alike).

V2 for cognatogen would be more beneficial than EK levels. Ek gives you exactly 1 feat(and it gives it late) at the cost of 1 SL early - pretty bad deal, especially for a caster who already struggles to keep up his caster levels on the curve. You don't really need that AB as you won't hit jack all without true strikes anyways before too long. Otherwise, yeah. People usually do it with draconic bloodline for more dice on the spellls.
I don't really like AT sorcs as it shafts spell progression a lot, so wizard does that job better, especially compared to sage who doesn't get anything special for his early levels. Thassilonian Glutton wizard would end up with more good things in life.

450 damage (horrid wilting) on mandragoa swarm with grandmaster rod, 400 damage to regular mobs with wail of the banshee...all in huge aoe.

provide your calculations. Because it doesn't add up. 30d6(E+M)+12d6=180+42=222 damage. 30d8(E+M)+12d6=240+42=282
And 400 damage is not enough to oneshot stull. You will have to recast it anyways. And ghosts are immune to it so you have to pick Stormbolts anyways. Also how exactly are you getting 400? 20*10*1.5=300. And that's assuming you used spell specialization on it. Then your other spells will lack two dice of damage.
I guess you can use sold souls and get dangerously close to oneshot HP. Eh... Either way, it's too many spells to do one job.

I am getting a 230 damage base on wail after it is specialized +sold souls. With Grandmaster Rod that jumps to 345. Sneak attack from AT10 adds another 60 to 70 or so in best case. so yeah around 400-415 damage in best case. Final difficulty check from a toon starting 17 Int +2 human, endgame with boken's elixer and cognatagon is 41 without rod of undeath and 43 should you get it as it adds another +2 dc to necro.

As a wiz and not a sorc one can get the base of horrid wilting a level higher to 240 with the spec and cloak. so there damage can top out at over 420.

max damage is not how the damage is calculated. You should calculate average damage, because that's what you are getting, after all. for a d6 it's 3.5 average, so 42.
In comparison, stormbolts with rod of flaming vengeance and GM rod on a fire dragon sorc top out at 240+42+32=314 average damage(that's without +damage per dice items), when horrid against plants will go for 240+42=282 average damage, so 11% less. Against most targets it's 180+42=222 damage or 27% less. Even against 30 fire resist enemies it will be on par.
And you still have no tools for killing ghosts/constructs and are picking two damage spells at 8-9, which obviously hurts your spell selection.
If you want save-or-die thing going it's better to run illusionist gnome with weird. It can kill all the same enemies than banshee can(and some more, actually) and doesn't rely on stacking dice at all, so you ran ramp stormbolts and/or rays.

stormbolts is a fine spell I know it's just I like acid focus for spell economy effeciency, you get more "acid" spells - especialy if you heighten them that are usefel. - acid pit lvl4 (can always be heightened later in game), acid ray ground attack (lvl 5), acid fog, caustic erruption (level 7) - caustic erruption deals damage 2 rounds so comes out very close to stormbolts already, just spread out on two rounds). hell I may even go sirrico as I do grab spell focus in evo to knock things flat.

On level 8 you can take strormbolts for backup anyways it is just a matter if you want seamantle before or not.

oh yeah wail does not have average damage it is all or nothing. they miss a fortitude save they take max damage or very near it- as long as there is no significant damage reduction it is always around 400 points damage. weird needs two saves...not a problem I guess at the very end when dc over 40 but illusion can be pita before that.

the 450 damage I got from a horrid wilting once was on a plant like creature...not sure how it happened but it was funny I did one shot the mandragoa.

at level 9 I like energy drain or whatever as the second spell to hw to just quickly mess up bosses.

EDIT: just to compare side by side I attacked a bunch of wild hunt goons at end with red dragon sorc focused on evocation/stormbolt damage and then repeated with a necro focused (same red dragon sorc) in wilting and banshee.

Stormbolts (specialized) had a max hit with sneak of 368. typically 345-360.
Banshee (specialized) 422. typically 386-411
Horrid Wilting (nonspeciliazed) 347. 330-345 range

Spell specialization +necro levels items allows Banshee to go beyond level 20 (no cap) in calculating damage.

Dazzling Display and Shattered Defense. Are those just for more consistent sneak dmg on touch attacks? Is it really worth 2 feats?

And why do you take spell specialization so early? It doesn´t raise spell DC so the only thing you get is 2 more rounds of Glitterdust.