This is my first guide, if you couldn't tell, it's for Sejuani: the Winter's Wrath. If anyone has any complaints, just alert me, and I will try to adjust the guide to be as accurate/helpful as possible.

Runes:
Seals (arf!): Greater Seal of Armor- Armor, pretty obvious as to why it helps.
Marks: Greater Mark of Attack Damage-I like to utilize a mix of AD and AP as Sejuani, mostly AP, but the extra 9 or 10 AD has saved me multiple times!
Glyphs: Greater Glyph of Ability Power ^^^
Quints: Greater Quintessence of Ability Power MOAR AP!!!

Masteries: I use a 22-8 combo for her (shocker, seeing as everybody uses 21-9), because I like to have my focus lie on her health and other defenses, but the Sorcery works wonders with her "W". And some extra AP never hurts!

Items:
Ninja Tabi is the best choice for boots when it comes to Sejuani, especially if you're going tanky (you are if you're using this guide). Building into a Sunfire Aegis makes your "W" epic, and helps you rack up CS like a baller! The Overlord's Bloodmail is crazy helpful if you're looking for health (you are). The Rylai's Crystal Scepter is nice for AP (and more health). The Randuin's Omen makes you even more tanky, and it's active is helpful in team fight. If you get to the point in the game where you can complete your build, the Frozen Mallet is a good choice, but not needed. If desired, you can change it for any item of your choice!

That's my build! I don't have any experience, so any tips/criticism is much appreciated! I will make updates as you deem fit, provided they are sensible. I by no means calling this built perfect, nor am I myself an expert, but I hope this helped!

*-I'm not sure why the guide says you'll end up with only 1980 health, in actuality, it will be around 5000.