I don't know honestly. I like Xerath, and this guide is a summary of my observations in blind pick play.

Pros

+ Extreme range. + Probably the best scaling abilities. + Long range stun. + Baron stealing Ult.

Cons

- Glass Cannon - Ult is a self root. - No escapes. - Item reliant.

Clarity: no use late game, as items solve your mana problem, but for lots of early poke, this is your spell.

Ignite: If you use your ult correctly, nobody should get away.

Barrier: If you're getting focused and flash didn't help, neither will barrier. Or will it? I like clarity but if you dont spam as much this is a better option.

Ghost: Xerath is slow, but you shouldn't need to run that fast. You have a stun and slow for escape.

Teleport: Maybe its just low elo, but i've seen ap mids take teleport. I guess for xerath it could position you for your ult, but its not that great. The extra mana from clarity will benefit you more.

Start: Doran's Ring and 2 Health Potion. against a hard lane, consider Crystalline Flask and 3 Health Potion.

Core:

Morellonomicon: Just get it. Mana regen, CDR, and AP. Its everything Xerath needs, plus the grievous wounds passive is great against tanks late game.

Zhonya's Hourglass: Threats from other lanes become significant after level 6, and you need the survivability if you want to be significant mid / late game.

Rabadon's Deathcap: Standard AP carry item.

Void Staff: AP and magic pen.

Sorcerer's Shoes. You need boots, and magic pen is usually more in need. It depends on what the enemy team is building, weather you can get away with Ionian Boots of Lucidity or not. Don't forget your enchantment, Enchantment: Homeguard.

Mana Surge Passive: Every 12 seconds, Xerath gets mana back when he auto attacks. Extra mana for hitting an enemy champion. Make sure to utilize this every chance you get. You're trying to spam abilities a bit early game, and this is what makes it possible.
Arcanopulse Q: its almost like varrus's Q where it charges up but does the same damage. This is your poke. Don't use it too often as it also helps you clear waves when you line up the minions. Take a point in it level 1 and 3 and max it first, as an early second point will help you more than the stun.

Eye of Destruction W: AOE damage, and a slow in the center. make sure to hit people in the center. you have no excuse to miss this if you stunned them. Take a point in this lvl 2 and max it second.
Shocking Orb E: Stun. Your stun is more effective at longer range like nid's spear. Despite recent nerfs to its max duration, its still a long stun. Does significant damage too. Take your first point in it at level 4, after the second point in q.
Rite of the Arcane R: Xerath's ult. Proper timing can result in a safe, long range dragon or baron steal, but generally its a long range execution tool after people flee. Save this for the end of team fights.

21-0-9 Standard as far as I know. I like the summoner spell cooldowns for those (Frequent) escapes.

Xerath is an AP caster, so I take flat AP quints and glyphs for the early ap. magic pen is a must. Take any defense you prefer, but scaling health is your best bet.

Your advantage is your range. When people want to intrude on your space, use your combo:

Q Arcanopulse , E Shocking Orb , W Eye of Destruction , and Q Arcanopulse again as the get their movement back. If they're low enough and running, R Rite of the Arcane 1 , 2 , 3 and you got yourself a kill.

Your Shocking Orb stops at the first thing it hits, but goes over walls including Anivia's.

If you found this useful please rate it, and if you didn't leave a comment about what you thought.

Thanks to jhoijhoi's Making a Guide guide!