Would be great, if you duo'ed with a support that could knock up or something like that, so you can get your third attack on Q in.

You would start buying "Doran shield" because your spell cost health = Sustain.

After that, you would normally rush a "Sterak's gage" so you can get more tanky and take some of that poke, your laner would probably throw out + the "Sterak's Gage" is scaling on max base damage + a shield that will proc with 30 procent of your maximum health, so you would end up with a decent damage, but your Q will carry the damage with its multiplying damage output.

I don't really know why i picked the "Trinity force" but its great to most of the champions, but on Mordekaiser it gives the stats you want. It gives you a nice little damage boost + the health you would need for "Sterak's Gage", some attack speed, the "Phage" passive that will give you bonus movement every time you basic attack. That is very important because of your Q, that you want to use everytime its possible on the enemy laner.

"Beserker Greaves" is an item i wanted to add cause of the movement speed because Mordekaiser is one of the champs i think with the lowest mobility in the game. + More attack speed, that you will need for Q.

You will need the "Warmog's armor" cause of the sick health advantage against most of the enemy champs, the passive on "Sterak's Gage" and the new incredible op passive called "Warmog's Heart".

Then we have the "Titanic Hydra" that give you +50 attack damage, even more health to the "Sterak's Gage" maximum health bonus + its let you damage 5 (+1procent of your maximum health) and 40 (+2.5 procent of your maximum health) as physical damage to enemies in a cone on-hit.

The last but not least we have the so called "Blade of the ruined king" that i find kinda good into this build, cause it give you the attributes like 25 attack damage, 40 attack speed, 10 life steal and the passive that will let you deal 8 procent of the enemy targets max health everytime you basic attack them. + you can use its "Active passive" to catch the enemy champion, that will steal 25 procent movement speed from them.

That was my guide on How to play Mordekaiser ADC, and i hope you find this guide usefull and you could leave an upvote, so other people get to know this build :)