Even with changes with the recent nerfs for on the Conqueror keystone, it is still a very strong rune for a select number of top laners. Mordekaiser is probably one of the best heroes that can abuse this keystone and smash any top laners that come in his way.
Mordekaiser's passive ability, Darkness Rise, allows him to stack Conqueror pretty fast and as long as you're in range of your target enemy champion, your passive ability damage will keep on going along with the stack on conquerors, resulting in damage to enemies while you heal yourself constantly because of Conqueror base on your damage output.
This makes him a pretty dangerous dueler in top lane, and considering the focus the bot lane is getting because the dragon is located on the bottom side of the map, you are pretty much always in a one versus one situation against your enemy top laner. And if ever you are in a 2v1 situation, you can always use your ultimate ability, Death Realm to make it a 1v1 fight again.
So, what do you need to build? It largely depends on the enemies you are facing. If the enemy is mobile and you have a hard time getting in range to them, Hextech Protobelt should be your first item. If the enemy has too much AD on their kit, build Zhonya's first. Here is a normal build on Mordekaiser.
Sorcerer Shoes -> ( this largely depends on how you want to approach the game. Sorcerer Shoes allows you to dish out more damage, if you want defense, go for merc threads or ninja tabi.) -> Hextect Protobelt -> Rylai's Crystal Scepter - > Liandry's Torment -> Zhonya's Hourglass - > Situational Last item
The build largely depends on who you are up against, so always understand the situation and adjust your build accordingly!
For the runes, here is what most pro players run today.
You can always switch out the scaling health for armor or magic resist depending on who you are up against.
Have fun playing Mordekaiser and smashing top laners!

Mordekaiser's passive ability, Darkness Rise, allows him to stack Conqueror pretty fast and as long as you're in range of your target enemy champion, your passive ability damage will keep on going along with the stack on conquerors, resulting in damage to enemies while you heal yourself constantly because of Conqueror base on your damage output.


This makes him a pretty dangerous dueler in top lane, and considering the focus the bot lane is getting because the dragon is located on the bottom side of the map, you are pretty much always in a one versus one situation against your enemy top laner. And if ever you are in a 2v1 situation, you can always use your ultimate ability, Death Realm to make it a 1v1 fight again.

So, what do you need to build? It largely depends on the enemies you are facing. If the enemy is mobile and you have a hard time getting in range to them, Hextech Protobelt should be your first item. If the enemy has too much AD on their kit, build Zhonya's first. Here is a normal build on Mordekaiser.
Sorcerer Shoes -> ( this largely depends on how you want to approach the game. Sorcerer Shoes allows you to dish out more damage, if you want defense, go for merc threads or ninja tabi.) -> Hextect Protobelt -> Rylai's Crystal Scepter - > Liandry's Torment -> Zhonya's Hourglass - > Situational Last item
The build largely depends on who you are up against, so always understand the situation and adjust your build accordingly!
For the runes, here is what most pro players run today.

You can always switch out the scaling health for armor or magic resist depending on who you are up against.
Have fun playing Mordekaiser and smashing top laners!