Introduction
Hi, this is my build for Sejuani; Whilst you feel it may be premature to talk about how to build her as she has only been out for one day, i beg to differ.
Sejuani is an EXCEPTIONAL ganker and a brilliant Tank. What she brings to the table is a LOAD of disruption is enemy move speed and attack speed while dealing a nice amount of damage at the same time.
Sejuani is an AP Tank. Building her Full Tank is ludicrous when you take into consideration how much damage she can deal.
Don't forget to comment and rate this build!
Pros / Cons
Pro's
Brilliant Tank
Great Ganking
Good team player
Great Crowed Control
Lots of Damage
can hold a lane on her own 1v1
Con's
Expensive build
Slow jungler
Needs a good laning partner
Sejuani Full Spec sheet with calculations!
Because the Spec sheet at the top lies and doesnt calculate things proporly, such as 
Rod of Ages
Base Stats;
Health - 1980hp
Mana - 940m
Speed - 315sp
Armor - 80.5ar
Magic Resist - 52.5mr
Critical Chance - 0%
Health Per 5 Sec - 22.55hp/s
Mana Per 5 Sec - 14.55m/s
Range - 125
Stats WITH Items AND MATERIES/RUNES;
Health - ((1980+630+500+330+370+108+30)x3%= 3948x3% = 3948 + 118 = 4066hp
Mana - (940+725+500) = 2165m
Speed - (315+70) = 385sp
Armor - (80.5+99+18+6+10) = 221ar
Magic Resist - (52.5+25+24+6+13) = 164.5mr
Ability Power - (80+80+15) = 155ap
Critical Chance - 0%
Health Per 5 Sec - (22.55+30+3) = 55.55hp/s
Mana Per 5 Sec - (14.55+15) = 29.55m/s
Range - 125
Tenacity - 35tn
Cooldown Reduction = (20%+15&+8) = 40%+cdr (40% is max)
Runes
Sejuani is your standard Tank when it comes to runes. However, most tanks may take full AD quints, you can do this too, but for early lane presence with abilities, switching for AP gives you a higher damage output through your W 
Northern Winds and a 2-1 ratio on your E 
Permafrost making you a high threat target!
The seals and glyphs are self explanatory; You're a tank!
The Marks however, are AD. why ? well you do need some damage from your auto attacks. after all, its your AA's that apply your passive! it also helps with last hitting minions and taking down towers. though scales out mid-late game.
Items
Your main Tank boots. you don't build much MR, so these boots are brilliant. However, if your enemy team is AD heavy, go 
Ninja Tabi, after the dodge change, they are better than ever!
You're AP and need HP... need i say more? This is a brillian item for Sejuani. 
Warmog's Armor is a viable substitute, but in no way will you hurt as much!
This item works brilliantly with her passive and helps break the enemy. Not only do you slow the enemy's move speed, but you slow the enemy's Attack speed too! this will utterly destroy the AD Carry.
More HP and More AP. All of your abilities deal magic damage, so they all apply the passive from this item. however, sometimes you don't quite get far enough, but you W Northern Winds may reach, this will then in turn slow them down, and make for an easier kill along with more damage and more HP.
I brilliant item. Though leave till almost last to squeeze the passive of the 
Philosopher's Stone. it also helps your team chase down those pesky enemies who run fast, or gives you a boost like ghost to get into the fight faster.
A tank is nothing without his team mate's beside them. This AoE buff passive makes for a tankier team meaning they can slay alive longer and have the upper hand against the enemy team!
Skill Sequence
Starting with her W Northern Winds allows Sejuani to farm minions better than most, just like 
Shyvana. this is also you're primary damage dealer scaling from 2% of your HP plus 40% of your AP. the base damage at level 5 is 36. This is per second for five seconds. OUCH!
Getting your Q/Dash 
Arctic Assault second is to easily apply frist to the target to slow them. it also helps for getting away and innitiating. This move can also be used to jump over walls!
Your skill sequence for attacking should be;
Q W E R. No joke.
Q to jump in an apply frost
W to activate your AoE DoT
E instantly after W to apply permafrost and deal damage
R to take down the high damage dealer or kill the person who is running away at the end of the fight.
Summary
Sejuani is an exceptional Ganker. Roaming is a strong place for Sejuani! so is jungling with ALOT of ganks.
Sejuani is the now GO TO TANK for me. huge damage output with great tanking abiliy.
please comment and rate! :D
- sgtn00b
*EDITS*
18/1/2012 - Build Created
21/1/2012 - Added Calculation sheet
21/1/2012 - Corrected spelling mistakes and formatting
Build Guide
Discussion (9)
Ignite if you need one in your team
Teleport if you are solo top
Smite if you wish to jungle. but be careful. Sejuani is a slow jungler. her ganks however, are second to none
