Not Updated For Current Season
This is roughly my attempt at a Mordekaiser tank build. Keep in mind this is only my second time trying to present a build on this website. Also this more for purposes of constructive criticism than a guide for others to fallow.
Masteries: I take a 09/21/00 mastery build for Mordkaiser. This is primarily a tanking build, but with a few minor adjustments to give a little extra punch to his abilities without removing his tanking power. Needless to say a full Defense build with a few ability power masteries (and of course cripple to help your exhaust) from your Offense tree.
Runes Red Rune = Spell Penetration (gives you a little more bang for your buck); Yellow Rune = Health (this will give you a little more staying power in those crucial early levels); Blue and Quints = Ability Cooldown (the more often you can use your abilities the more shield power you will keep and the more you will utilize your spell penetration)
Ability Progression I take one of each ability to start and then go by a priority of Children of the Grave > Siphon of Destruction > Mace of Spades > Creeping Death (Mostly I think this falls under personal preference, but I think SoD is one of your best farming abilities so Maxing it early is huge. MoS seems to be the second most effective and CD is good but not nearly as nice as the others. CotG is your great gank kill combined with ignite you can easily finish off opponents that are close to death and getting away.
Summoner Spells I chose Exhaust and Ignite for one main reason, and that is a good opponent can get away before you can finish them (or at least I have this problem alot). So using ignite and CotG when an opponent is low can help guarantee you that kill. Exhaust is ofcourse used for both catching up with the opponents and turning the tide of a 1 on 1 (because of the temporary blind effect).
Items First item I lead with is Regrowth Pendant (no matter the build this should be used and worked into something useful); Second I will get the mercury treads (less stun and snare time = more ability using time and more shield power); Next I will get the Warmog's armor that I started with the Regrowth Pendant doing this ASAP is crucial so that you can get all of Warmog's armor stacks up and gain some real staying power; After Warmog I go with Phage because the + to health along with the chance to slow your enemies is very helpful (considering changing this with Rylia's Crystal Scepter); Next try to get Warden's Mail and Stark's Fervor to really polish up your Hp/5 power and easily be able to handle turret fire without creep fodder; By this point chances are the game was already long over, but on occasion fights last seemingly forever. When this happens finish Warden's Mail into Randuin's Omen and finish up Phage into Frozen Mallet (if you go Rylia's Crystal Scepter than ignore Frozen Mallet). By now tanking a tower shouldn't phase you and it will take atleast three-four good opponents to take you down (assuming you have full health) or even make you change direction for that matter.
Well I hope I have throughly explained my Mighty Morde build. Please Please post comments anything that would help me improve is welcome.