Sorcerer's Shoes (if you buy Mercury's Treads get runes quintessence of Magic Penetration) - Now Hex Revolver (Shoes, Hex Revolver, Sorcerer's Shoes)- Warmog's Armor - Will of Ancients - Rabadon's Deathcap - Force of Nature - Guardian Angel.

Why Warmog's Armor? I love the slow of RoE but Mordekaiser is focused almost always

Force of Nature and Guardian Angel? Mordekaiser isn't tank like Malphite but maybe the team dont have tank or you need ressist more. You can buy Deathfire Grasp or Lich bane (I love Lich Bane in Mordekaiser)

You can change Force of Nature-Guardian Angel by Abyssal Scepter and Zhonya Hourglass

Only if the team don't have tank you jump first with your shield full (if possible), when you have half or more of life use ULT, you will be attacked with ignite so you can't save it for last, use the ULT against Ranged AD. Remember the E and Q reload your shield, dont stop and escape with Flash if you are gonna died !

You can't play safe in team fight but in Top is necessary play safe the first 6 lvls, maybe more... Ward the lane, Mordekaiser is really good but junglers like Lee Sin can destroy you shield and escape easy.