This build was designed to provide the ability to tank throughout the match and turn team fights
from 5v5 to 6v4. Late Game you even have the ability to tank turrets down i don't suggest doing so alone as you will be extremely easy to pick off if you do. Ghost and Exhaust are useful both offensively and defensively for either chasing down kills or running away.

The focus of my runes are to help with survivability through dodge and Magic resist while providing Mordekaiser's abilities Damage by cutting through enemies with Magic penetration.

My masteries are 0/21/9 making morde a tank and adding some utility for easier item gain

This build was designed around having a smooth item selection process, focus on last hitting mobs with your abilities and above all else stay alive. Start out with a Regrowth Pendant and a Health Potion, as Morde's abilities use health you will need the health regen to stay in the fight the health potion is for if you extend yourself to far. Your first cash in will be at 850 gold to pick up your ninja tabi at about lvl 5-6 unless someone was nice enough to feed you.
Then at 750 for an Avarice blade note that at about this time you will be vulnerable to high dps Champions until you get your Warmog's armour, once you do don't be afraid to jungle for a bit as monsters also count for warmogs stacking ability ignore the buff giving mobs as they really provide no lasting benefit for morde and are probably better suited for other champions.
Now here is the 1 chance for deviation in my build you can either get Guardian Angel or Malady at this point in the Game if you notice the enemy champions are not doing considerable damage to you get Malady as it will help you push harder and get turret kills. Althought i recommend getting Guardian Angel first because it has a considerable higher cost.
From here on out its all AP morde's Attack damage is decent to begin with but you want to stack as much ability power as you can with the slots available Voidstaff is an excellent choice for the Magic Penetration and Rabadon's Deathcap gives considerably more. once the Item build is complete feel free to sell Avarice Blade to stack more Ability Power such as Abyssal Scepter all the Ability Power turns Mordes Ultimate into a Scary ordeal for any unlucky soul caught in his path as it does over Half there total health Over 10 seconds