Mordekaiser really does not need it. You don't need to be tanky early game, or you will lose it, literally.

The reason why I build Warmog's Armour early game as Mordekaiser simply because you will have incredibly survivability in early game where your shield just doesn't cut the mustard, when you get to level 18 and you have a 630hp shield i do admit that your warmogs becomes wasted, however at the same time, with that early game survivability you can take more risks in the lane and get kills, it doesn't take many kills to make mordekaiser unstoppable, i'm currently making up my mind if its worth selling your warmogs armour once you've made your 6 item build to buy a good AP item (most likely a Hextech Gunblade for the spellvamp that will make up for your lost health regen.) however by this time in the game you've either A) Won or B) managing to carry your whole team who fed hardcore but the enemy tried a foolish gank with less than full health on morde (which you can thank warmogs for). I will try and find out if selling your warmogs becomes more profitable but still having its effect for long enough to not need that babysitting.

Warmog's Armor.

i was going to down vote but you have a good point and your build isn´t very different from mine when i started playing morde so i gave you a +1 check my build if you want another pov for morde

P.S i wouldnt take warmog if your are alredy buying crystal scepter maybe i would change it for FoN or for some spell vamp to keep your survability high