Mordekaiser is one of bests solo top champs, because of his persistance, his nice farming habilities and his considerable damage. In this build, I make him more tanky, because I use to play with a damager jungler. Anyway, you can make him more ap if you want.

He has nice damage spells, with syphon you can mantain the pasives armor and get few damage, with the creeping dead become difficult to kill, and with the maze farm nicely.

I take magic penetration runes, in top are bery useful, as well as ability power per level runes, conbinated with the quintessences give mordekaiser a good damgage for all the game, and finally hp runes , required to stay at top.

I take all the ability power masteries as well as the basic ones of defense, for having a few more hp and a consistant ap.

First of all, i take life regen, it is very useful in the line because of the passive, and the cost of hp of your spells. With the life regen , you can saty long at top, and if your hp goes too low, take the potion. You will stay in line enough to get many money, and with the spell vamp your hp problems in line will disappear. Mordekaiser has a big problem: he hasn´t any stun hability, and that´s why rylai is so important. With warmog, you will resist a lot, and with the final ap items, your damage will be very nice even though your 3000 hp.

I take ignite because it is very good convined with the ulti, and it is useful against some top champs (mundo, irelia, nasus etc...)
I take flash because as you all know it is really useful for scaping or killing.
Taking teleport isn´t a good idea, your lane persistance with this guy is very hight. Ghost can be a good chance too.

Pros:

-Nice persistance in line
-Good damage on spells
-Good hp
-Difficult to kill (vamp)

Cons:

-Can´t catch enemies easily
-Few range
-It´s always banned

Mordekaiser´s team work is focusing the carri, with siphon and if you get near enough, the mace of spades get carri´s hp low, and if you catch the carri with the ulti, the teamfight uses to be won. To iniciate, throwing siphon and creeping dead on you will give you a good survive chances, with teh vamp and the passive. Use the maze for more specific targets.

Farming with morde is easy, if the enemy is in the line, use siphon from the behind to kill the minions, and if the enemy is weak, use all your spells and the farm will be done.