This build, together with the Meterorb build, is the most viable sorc if you want to play solo at Hell difficulty. The gameplay will be more active than for the Meteorb, since CL is a non-timered skill. Like the Meterorb sorc, this build is also suitable for MF:ing (Magic Finding) although I didn't use my FO/CL for this purpose. For new players, or when you start playing your first char after a ladder reset, I would recommend the Meteorb before the FO/CL since she is more equipment-demanding.
Stat points
Strength: enough to wear your equipment
Dex: Enough to gain full block with your shield (see Dottie's comments on blocking in the Blizzard sorc guide).
Energy: 100-125 depending on how much +mana items you have
Vita: Enough to have at least 300 life (including +life equipment) when you enter Hell. You can add more if you die a lot, but it is better to use +life items.
Skill points
1 in Warmth
1 in Teleport
1 in Static Field (optional, it's convenient in Normal and Nightmare but not necessary)
1 in Energy Shield (only if you have problems surviving, I did not use it)
20 in Frozen Orb
7 or 17 in Cold mastery including the bonuses from your equipment
20 in Chain Lightning
20 in Lightning Mastery
the rest in Lightning
if you get high enough lvl to max Lightning, you can put the rest in Charged Bolt (synergy to CL), Frozen Armours (if you don't have them on a weapon swap, which I recommend in order to save skill points)
Put a point in Warmth early on, mana is always a problem for a young sorc and this build will be increasingly mana intensive since you are going to spam CL all over the place. Until lvl 12, put one point in all prereqs. At lvl 12, put some points in Lightning so you have 5-7, and use this as your main skill until lvl 18 when you get CL. From lvl 19-30, put points in the prereqs and some more in CL, but save 2 points so you can put 1 in FO, 1 in Cold Mastery and 1 in Lightning Mastery as soon as you reach lvl 30. From now on, you life will be easy
Through Nightmare, you can alter between putting points in FO, Cold Mastery until you have 7 (with +skills equipment), CL and Lightning Mastery. After that, max out Lightning. You should now be around lvl 85 or so (depending on how many +skills you have to reach 7 in Cold Mastery). If you get this far, you can either choose to take Cold Mastery to 17, or to put the rest of your points in Charged Bolt to increase your CL damage. If you plan to do Meph runs for MF, choose the former alternative, if you play areas with hoards of monsters, choose the latter.
Equipment
You will need a lot of mana from the beginning of the game, so use socketed items with sapphires to increase your mana pool, and skulls to increase your mana regeneration. Don't be afraid to use up your gems, gems are very common in D2. You also need a 3-socket shield with diamonds (a 3D shield) in order to get resists.
The most important mods to look for on items is +skills and Faster Cast Rate (FCR). How fast you can spam your Lightning and CL will depend on your FCR since it is a measure of how many frames there will be between your casting (the game operates in 25 frames per second.). Just like with IAS and other mods, there are certain breakpoints, so there is no use achiving let's say 100% FCR, since everything between 78-116% will result in 13 frames casting for Lightning and CL. Not all skills have the same FCR breakpoints, CL and Lightning has one table, whereas other important skills such as Teleport has another table.
Frames/FCR for Lightning and CL
19 - 0%
18 - 7%
17 - 15%
16 - 23%
15 - 37%
14 - 52%
13 - 78%
12 - 117%
Frames/FCR for other skills:
13 - no FCR
12 - 9%
11 - 20%
10 - 37%
9 - 63%
8 - 105%
7 - 200%
For most players, it's fine to aim for 63% FCR, which gives you 14 frame CL and Lightning and 9 frame Teleport and other skills. 63% is quite easy to achive with rings, ammo, an orb and a good armour.
You should also look for +mana and +life, and resists.
Suggestions for the average player:
Weapon: Wizardspike, rare sorc Orb with +skills and resists.
Shield: Viscerataunt sck with perfect diamond and Moser's Blessed Circle socketed with 2 perfect diamonds are very good. Otherwise a 3D shield with high block, Sigon's with perfect diamond.
Armour: Although it is relatively easy to find and very cheap to trade for, Skin of the Vipermagi is one of the best armour you can get for the FO/CL.
Helm: Tarnhelm is very good with both +skills and MF. Runeword Lore, Peasant's crown or a rare circlet with +skills and resists.
Belt: Nightsmoke, look for resists and mana.
Boots: Look for MF, faster run/walk and resists.
Gloves: Frostburn, or rare gloves with FCR, +mana and resists.
Amulet: Rare or magical amulet with +skills.
Rings: Look for +mana, FCR and resists.
"Godly", best possible equipment
Weapon:Death's Fathom
Shield:Lidless wall, Whistan's guard
Armour:Ormus with +3 to CL/Lightning/Lightning mastery, Skin of the Vipermagi
Helm:Rare circlet with +2 sorc skills and 20 FCR, Nightwing's veil
Belt:Arachnid Mesh
Boots:rare with good mods like high resists, faster run/walk, life, or other mods you need
Gloves:Magefist, Dracul's, crafted blood gloves with 20 FCR
Amulet:Mara's, crafted +2 sorc skills and 20 FCR
Ring 1:Stone of Jordan, 10 FCR
Ring 2:Stone of Jordan, 10 FCR
On weapon switch:Call to arms and Lidless eye
In inventory::
x10 Lightning Grand Charms w/life
x1 Annihilus
x9 Resist/life small charms
Mercenary
The best merc for this build is either a Holy Freeze merc or a Defiance merc. Your merc needs good equipment to survive, so look for armour and helmet with high defense, damage reduction (DR), and resists. Rockstopper and Shaftstop are excellent. He also needs a good weapon, so look for etheral rares or uniques with high damage (merc's can use ethereal items forever, and etheral weapons have a damage bonus whereas ethereal armour has a defense bonus). He must also have life leach, so either socket your weapon and put an Amn rune in, or use items with life leach.
Gameplay
Since both Frozen Orb is a timed spells that freeze for a long time but do little damage, and CL is a non timed spell that deals a lot of damage, the idea is that you open with FO to freeze monsters, and then kill them with CL. You can go FO-CL-CL-FO-CL-CL until monsters are dead. CL has a very long range, it reaches outside the screen actually. If monsters are lumped together or if there is a single or just a few powerful monsters, use Lightning instead of CL.
