Hi!
If you are reading this guide it means that you want start playing Mordekaiser, The Master Of Metal.
I created this guide whit my high knowledge about Mordekaiser as i'm playing it as my favourite champion and i'm very good whit it.
I hope that you will find it useful and try it before downrate this guide :)

Pro:
One of the best farmer in the game
Really hard to kill
The best ultimate to finish low hp champions
Cons:
Very sensible to cc
If Morde doesn't build up is shield fast he will easly die
It is everytime banned in draft pick mode in ranked games

The 9-0-21 Masterie is the best choice for Mordekaiser.
The Archaic Knowledge is a need for Morde as you do magic damage whit all your spell and you should take it before the utility tree if you have not a level 30 summoner.
Then from utility you take golds, CD reduction for spells and summoner spells, health regen, movement speed, time reduced dead and increased exp.

BEST CHOICE
Flash: One of the best choice for every champion, it is the best way for escaping enemys and kill the ones faster than you.

Ignite: Another common great summoner spell, it allowe you to kill more easly low HP champ. You should combine your ulti whit ignite so that other summoner spell like heal or spell like soraka's astral blessing have half effect.

OTHER GREAT CHOICE

Ghost: even if is lower than Flash as escape mechanism is maybe the best chasing summoner spell in the whole game. Take it if your summoner have lower level than 12 or if you don't like use flash.

Exhaust: whit exaust you can ensure that enemy won't flee/chase, but only if they don't have flash. If you are a fan of Exhaust you can take it and you should take out of your masteries the point of deadliness and put it in to cripple.

WORST CHOICE

Heal: Summoner spell used by lows and level 1 summoners. Good only for first blood and early game, useless in mid and late game.(If you are a level 1 summoner i want let you know that is much better take teleport and ghost than heal)

Teleport: Well, is good for save turrets and fast return on your lane in the laning phase, aniway i think that there are best choice for Morde as you have your Will Of Ancient to regain health instead of recall.

Cleanse: yes it clear out all your Crowd control effect but this spell alone won't save you.
-SUMMONERS SPELL THAT MORDEKAISER MUST FORGET-
If you dare use someone of this spell whit mordekaiser after read this build i will come to your PC and kill you slowly...and you will be banned for leaving game :D

Revive: One of the worst spell for tanks. Big cooldown 10 minutes. You have mastery point? 9 minutes. And in this build morde is not even a tank.

Smite: Morde jungler? Pfffff...

Fortify: I tell you that this is not a Morde tank build!

Clarity: Trololol Morde have no mana...is much batter smite...

Rally: Maybe is the most useless summoner spell in all league of legends for all champions...Maybe morde can need more clarity :D

I start whit an amplyifing tome because it give to morde a little more ability power that is transformed in more temporary shield and more minion kill. i also recommend you to buy two healing potions that allowe you to stay in lane for long time

As soon as you can come back and buy your Extech Revolver that let you have 15% spell vamp that will decrease your spell health cost and give you more survivibility.

Then start build your sorcerer's shoes that give you magic penetration.

If you are getting easy kill you should take the Mejais soulstealer as your third item.

The Will Of The Ancient is one of your most important item as allowe your to regain health from your spell instead of loose it. More target you hit whit your spells more you get healed. More AP you have more you get healed.

The Relais Crystal Scepter is another item needed from morde as give you slow on targets hitted by siphoning strike and maces of spades.

The Rabadon's Deathcape is one of the most important item for AP champs as give you 140 AP (20 more than the items who construct it) and permanently increase your AP from runes, masteries and items by 30%

The Void staff gives you high magic penetration and should be prioryzed if you are getting feeded and enemys who are not n00bs start build up a Force Of Nature to increase MR

-REALLY IMPORTANT-
The Mejais soulstealer is a optional items so if enemys are focusing you and killing you because you are feeded you should buy items to increase your survivibility like Zhonia Hourglass or Guardians Angel

The Ulti is obviusly upgraded everytime Morde reach lv 6-11-16. You can use it to deal Dots at a low hp champion, turn teamfight from your side as enemys loose a champion and you earn a minion that have champion stats, take time while you are fleeing from enemys as it steals enemy hp restoring yours, you can waste it if you have half hp and you want regen it because you are solo-laning as one of your teamates is jungling and you can't recall.REMEMBER THAT YOUR PET AFTER 30 SED DIE AUTOMATICALLY SO FEEL FREE TO LET HIM TANK TURRETS AND TRY TO KILL LOW HP CHAMPS UNDER TURRET!

1st choise from normal spells: i prioryze first Siphoning strike as is your farming,(quite)ranged and harrasment skill. it also give morde an high ammount of shield from the racial if used correctly on a wave of creeps.

2nd choice from normal spells: it is maces of spades because it is another AoE in used against multiple targets and also deal high damage if used on a single enemy that can be a champ in a 1vs1 fight. I use it most of time aster i used Siphoning strike on a wave of creep to ensure last hit on several minions

3rd choise spell is creeping death that is a nice spell aniway. use it on minions when approach enemy champs to deal damage or use it on yourself and allies to help them surive from enemys and deal damage.

Thank you for read my build and i hope that whit this you will be able to deal Pentakill's!
Just remember that even if you are using a nice build battle can be lost for plenty of reason.
Think about that before downrate this guide :D
GL&HF