This is my Mordekaiser: The Master of Metal guide. First of all, I just want to say off the bat, THIS IS NOT A TANK MORDEKAISER BUILD. If you want a tank build, find a different one and don't downvote because this one isn't a tank. I build Mordekaiser as a tanky mage, capable of taking harassment without flinching and dealing some damage.

Mordekaiser is a mage with lots of health who can stand heavy punishment. He excels at farming, supporting allies, and turning the tables in a teamfight.

Runes are good on pretty much every champion. With Mordekaiser, however, runes are not essential. He doesn't need typical mage runes, which deal with mana. To be perfectly honest, I don't have a Mordekaiser Runeset. But here are the ones I would probably use if I did.
Greater Mark of Magic Penetration: Magic Penetration, good on any mage.
Greater Seal of Magic Resist: Magic Resistance, which is generally good for anyone, especially tanky champions.
Greater Glyph of Health: Flat Health, for some early game survivability.
Greater Quintessence of Health: More Flat health, for more survivability.
If you don't have these runes, don't feel like you need to go out and get them. If you really want some, go with tier 2.

You can obviously see what my masteries are, but if for some bizarre reason, you can't, I'll briefly explain them. I take 9-0-21 masteries. On the Utility tree, I try to avoid anything dealing with mana, but it's not entirely possible. On the Attack tree, you can either go to Magic Pen or spec Ignite

I take Teleport and Ignite most of the time. On The Twisted Treeline, I use Exhaust instead of Teleport. Teleport helps you get around quickly, and sometimes get kills by porting to wards, mushrooms, etc. Ignite has excellent synergy with Children of the Grave, in which they are both DoT.

Although there are six items listed on this build, there are many other situational items. I will explain the core items and the other ones here.
Mercury's Treads: Magic Resist, Tenacity, all good. Other boots you can get are Boots of Swiftness, and Sorcerer's Shoes.
MAGE ITEMS:
Rylai's Crystal Scepter: Your main core item. Health, AP, and a permaslow on any enemies you are facing.
Abyssal Mask: Health, Magic Resist, and reduces enemy MR? Me like.
Rabadon's Deathcap: I have never actually gotten this far to actually get this item. But when you do, you get tons of AP, making all of your moves be CRAZY.
TANK ITEMS:
Sunfire Aegis: Health and Armor, combined with a mini Creeping Death. Very good.
Force of Nature: The item that most beginning Mordekaiser players rush. Yes, it gives MR and Regen and Speed, but that isn't helpful without health first. I get it near the end, or when there are lots of magic users on the opposing team.
Warmog's Armor: Loads of health with a some Health Regen.
Thornmail: Useful vs. heavy AD teams, such as Master Yi, Tryndamere, etc.
These above items (The Tank items) are interchangeable and rely heavily on the enemy team.

Enemies despise this ability, especially the ones laning against you. A zero cost shield that absorbs all damage (even Ignite! :D) that is generated by doing what Mordekaiser does best! Spamming his abilities!
Always try to keep this shield at full strength. Do so by doing this combo to minion waves:
Siphon of Destruction>> Mace of Spades>>Run into the middle of the remaining minions and put Creeping Death on yourself. This will effectively pop your Iron Man shield up to full strength. This shield is the reason many people say Mordekaiser is a tank. I however say it is a feature that makes him an even better mage. With this shield always up, you will take no damage from anything but yourself. It is always funny when someone turret dives a seemingly low health Mordekaiser only to find that his shield is full strength. Then they die.
Another great way to charge your shield is simple and amusing. Put Creeping Death on a Siege Minion that is pulling up to the enemy turret. You will hurt enemy minions, possibly champions, and charge your shield passively. Once, with this tactic, and the help of basic minions, I dropped Teemo to half health.

Iron Man is Mordekaiser's passive ability. 25 / 27.5 / 30% of the damage dealt from abilities is converted into a temporary shield, absorbing incoming damage. Maximum shield strength is 90 + (30 x level). The shield decays by 3% per second.
As I said earlier, this ability is great, and it allows you to take harassment without taking any actual damage.

Mace of Spades is Mordekaiser's Q ability. (Active): On next hit, Mordekaiser swings his mace with such force that it echoes out, striking up to 3 additional nearby targets, dealing magic damage. If the target is alone, the ability deals 75% more damage.
Additional target radius: 600
Cost: 25 / 32 / 39 / 46 / 53 health
Cooldown: 8 / 7 / 6 / 5 / 4 seconds
Magic Damage: 80 / 110 / 140 / 170 / 200 (+1 per bonus attack damage AND +0.4 per ability power)
Single Target Magic Damage: 140 / 192.5 / 245 / 297.5 / 350 (+1.75 per bonus attack damage) + (+0.7 per ability power)
This is a good ability, but definitely not Mordekaiser's best. It does damage to one target, then 3 others. It does bonus to single targets. It doesn't do a lot of damage, but it can be helpful in farming and teamfights.

Creeping Death is Mordekaiser's W ability. (Active): Unleashes a protective cloud of metal shards to surround an ally, increasing their armor and magic resistance and dealing magic damage per second to enemies in the cloud for 6 seconds.
Range: 750
Cloud radius: 250
Cost: 26 / 32 / 38 / 44 / 50 health
Cooldown: 20 / 18 / 16 / 14 / 12 seconds
Armor & Magic Resist: 10 / 15 / 20 / 25 / 30
Magic Damage: 24 / 38 / 52 / 66 / 80 (+0.2 per ability power) per second.
This ability is very fun. It's got a relatively short cooldown at high levels. Doing damage over time while boosting resistances? It's TIME TO SHRED, baby! When you get Rabadon's ("if", I guess) it does lots of damage.

Siphon of Destruction is Mordekaiser's E move. (Active): Mordekaiser damages enemies in a cone in front of him, dealing magic damage. For each unit hit, Mordekaiser's shield absorbs additional health.
Cooldown: 6 seconds
Range: 700
Cost: 24 / 36 / 48 / 60 / 72 health
Magic Damage: 65 / 105 / 145 / 185 / 225 (+0.6 per ability power)
Additional Shield Health: 1 / 2 / 3 / 4 / 5 per unit hit
My favorite move as Mordekaiser! (Excluding his ult, of course) It charges his shield very well, and has a good AP ratio, and does decent damage. Eventually, you can one hit the caster minions. And it gives extra shield the more enemies you hit? ME LIKE!

Children of the Grave is Mordekaiser's R move and his Ultimate. (Active): Mordekaiser deals damage to the target and curses it for 10 seconds, stealing life. Damage is equal to a percentage of the target's maximum health. If the target dies while under the effect of the curse, their soul is enslaved and will follow Mordekaiser for 30 seconds. During this time, Mordekaiser gains 20% of their ability power and attack damage. The spirit gains 75% of Mordekaiser's adjusted damage, ability power, and health totals.
No cost
Range: 850
Cooldown: 120 / 105 / 90 seconds
Initial Life Stolen (Magic Damage): 12 / 14.5 / 17 % (+0.02% per ability power)
Curse Life Stolen (Magic Damage): 1.2 / 1.45 / 1.7 % (+0.002% per ability power) life per second
Mordekaiser's Ult is, in my opinion, one of the better ones in the game. You do some nice DoT and turn a 5v5 into a 6v4! And if you use it on a main DPS, like Tryndamere or Caitlynn, for example, you can wreck everyone in sight and get double kills! Or Triple kills! Or if you use it on a tank, like Rammus or Malphite, you can tank turrets and push quickly.

Mordekaiser, the tanky AP kind, has odd strengths. He, in my opinion, is best at early and late game, while middle is not great. When you first start the game, buy a Regrowth Pendant and one Health Potion. Run to top lane or bottom lane. I don't really know how one would play Mordekaiser mid, but you can try it if you want. This guide is based on being in a 2v2 lane. Get Siphon of Destruction first. This is your best shield charging ability, and is very good at harassing. When you set the cone, set the tip of it on the enemy melee minions, so the main cone hits the caster minions. After you use that, just try to last hit.
Next, you can decide which ability to get next, Q or W. The Q, Mace of Spades is good at damaging opponents, while W, Creeping Death is great at charging your shield. The important thing is just to alternate between the two in leveling. Use Mace of Spades whenever it is up. Creeping death can either be used on a DPS when they dash in, or on yourself to charge your shield (also on Siege Minions for the same purpose).
When you hit Level 6, you grab your Ult, Children of the Grave. Use this on low health champions in conjunction with Ignite and all your other spells. Then you have a ghost, to either help farm, kill the other champion, or hurt/tank the tower.

During Middle Game, Mordekaiser has many options. Firstly, he can remain in lane and farm up, allowing him to get "minion fed", so he gets more items. Secondly, he can sort of "roam", going from lane to lane, helping allies fight and farming. You might even completely switch lanes. Determine with your team who you are going to focus, and during teamfights, place your Ultimate on them (Or the main DPS, if they are different). When you use your ult, be sure to use ignite with it. By now, you should have Rylai's, so you can chase easily.
During major teamfights, spam your abilities as much as possible. If you need to, you might actually need to tank a bit for your team. Most likely, you will be the second most tanky champion, so sometimes that role falls to you. However, just because you have to sometimes tank doesn't mean you can't try to dish out as much damage as possible. Use any skills you want in any sequence. It doesn't really matter at this point. The only exception is your ult. Use the same combo as usual for that.

Many people think that Mordekaiser should be a full tank. Sure he can take damage rather well, but he has no initiate. He can tank if it is absolutely necessary, but I don't recommend it.
With a ghost, Mordekaiser can actually be a very good pusher. Even without a ghost, he can backdoor turrets. I've done it myself and seen it done multiple times.
He shouldn't, however, be a MAIN mage. He doesn't do enough damage to champions for that, but he is a very good Tanky Mage.

Mordekaiser's ghost retains all of its on-hit effects, like Madred's or Wit's End.
Ghosts can still have Banshee's Veil on them.
Ghosts use that champion's passive, such as Warwick's Eternal Thirst.
All of Mordekaiser's moves are based on heavy metal songs. (Iron man: Black Sabbath) (Ace of Spaces): Motorhead) (Symphony of Destruction: Megadeth) (Creeping Death: Metallica) (Children of the Grave: Black Sabbath)
For more Random facts, go to http://leagueoflegends.wikia.com/wiki/Mordekaiser_The_Master_of_Metal/SkinsTrivia

Well, I hope you enjoyed this build, and have great success with it. Mordekaiser is a very fun champion to play, and I hope you enjoy him as much as I do. Feel free to post comments or suggestions. But please try the build before you downvote it. If you don't like it, tell me why so I can fix it. That's what this is here for, after all. I just want to add, with this build, I have a 4:3 win loss ratio. Or something around that. Anyway, it works for me, and I hope you share my success.

If you want a link to my other build, Master Yi: The 3v3 Shredder, here it is:
http://www.mobafire.com/league-of-legends/build/master-yi-the-3v3-shredder-64596