^ this seems spot on to me.

nonononononononononononononononononono.

Runes: Greater mark of hybrid penetration (or Greater Mark of Attack Speed), Greater Seal of Armor, Greater Glyph of Magic Resist (or Greater Glyph of Cooldown Reduction), Greater Quintessence of Movement Speed.

Rush/Core: Spirit of the Ancient Golem, Ninja Tabi (mobility is alright, you can leave them if you want), Sunfire Aegis, Spirit Visage.

Skill Sequence: W-Q-W-E-W-R-W-E-W-E-R-E-E-Q-Q-R-Q-Q

Masteries: Remove Bladed Armor and Reinforced Armor . Use those two points for Block if you want early game protection or finish Tenacious (I think Moba messed up the names and switched Tenacious with Legendary Guardian lol) for teamfight stats. Scout is pretty poor, take mana regen or fast recall.

Summoners: Flash. Flash+ Arctic Assault or Flash+ Glacial Prison is better for ganks and teamfights than Ghost. Also you're a weak duelist early so if you get caught in your jungle you need to be able to flash over a wall to escape.

BBcode: Nonexistent. Use the links Maintained gave you.

Thank you. I mentioned similar to volibear "in that she scales with health", so I compare them around that. I will add in BB code and possibly update it for an actual AP build asap.

A few things regarding your guide:

• This isn't an AP guide, call it perhaps, an AP-Offtank guide? Not too sure though.
• For your runes; Greater Quintessence of Percent Health and Greater Seal of Percent Health are terrible. Same goes for Greater Mark of Ability Power. If you want to deal more damage using Marks use Greater Mark of Hybrid Penetration.
• You should be starting Hunter's Machete with 5x Health Potion, not just one.
• Warmog's Armor sucks as a core. It sucks in most cases as well because of all the % health damage from items which is commonly used nowadays. It is also more expensive than both Sunfire Aegis and Spirit Visage.
• Liandry's Torment shouldn't be a core, it should be an option to take only when you're ahead, or else you'll set yourself behind.
• Frozen Heart > Iceborn Gauntlet. And if you tell me you prefer Iceborn Gauntlet for the slow, I sadly have to tell you that Sejuani already has built in heavy croud control and a slow.
• Your skill sequence sucks. Stick to a single skill and max it, you have no reason to take turns leveling both of them up.
• I disagree with Ghost. With Flash you can set up decent ganks or catch someone off guard easily, especially if you combo it with Arctic Assault.
• Quoted:

  Sejuani is similar to Volibear
  Not at all, Volibear doesn't have the extraordinary croud control Sejuani has but in return he can deal massive damage even while going fully tanky. Volibear is also a better at ganking pre-6.
• Your guide lacks BBcode , here read this: Making a guide

Good luck summoner!