Not Updated For Current Season
Your skills use health, more health regen = more skill usage + Longer lane staying = More farm.(Later upgrades into Force of Nature)
2. Ability Power + Spellvamp helps you deal damage while healing any damage dealth to you in lane.(Later upgrades into Hextech Gunblade)
3. Magic pen means your Skills hit harder. You could change those to Mercury Treads if facing an Heavy CC team.
4. Great Health Regen AND Magic resist against those AP carries. 8% Move speed is also nice as Mordekaiser needs to get close to do damage. Can be replaced by (which later upgrades into ) if enemy has mostly AD carries
5. Ability Power, more Magic resist and -20 magic resist to enemy champions close to you. Can be replaced by if you think u can get lots of Kills/Assists with out dying.
6. Health + Armor = More Survivability AND the Passive 35 damage per second works well with your .
7. More Ability power and Spell vamp + some Attack Damage and Life steal. Now you might ask why this over well since you are going to be fighting in mele range anyway why not dish out some extra damage with mele atack's? Most important reason tough is its Active(As you might know Mordekaiser lacks any CC this compensates for it slowing your target by 50%).
8. Gives 25% Cooldown reduction (which is HUGE) it also gives you Ability power wich is always nice while 50% Attack speed is a nice bonus to your Auto atack's and Life steal.