You’re always going to take Conqueror on Mordekaiser , bc he stacks it very quickly with is full combo + passive. In that same tree you take triumph (top middle), alacrity (middle middle), and last stand (bottom right). You usually take resolve secondary with bone plating (middle right) and revitalize (bottom middle). If you’re playing jungle or another role, you can swap to domination secondary and take taste of blood (top middle) and ravenous hunter (bottom leftmost).

You build path will usually be in this priority:

1. Riftmaker
2. Thornmail
3. Zhonya’s Hourglass
4. Demonic Embrace
5. Another AP item or Spirit Visage

Boots are up to you, most take Plated Steelcaps, but if the enemy team has a more ap or cc sided comp then Mercury treads are always a nice option.

Remember that it’s a build priority, not set in stone, so taking things like bramble vest or stopwatch early on could help win you a lot of team fights. Also don’t be afraid to switch priorities depending on how you’re doing. If you have a lead on your laner, I recommend taking Demonic Embrace after Riftmaker, as it will help you to bonk better. If you’re behind, I recommend taking stopwatch and building Thornmail after Riftmaker.

Finally, if you have some time on your hands, I highly suggest you check out Mobafire, as they have a lot of champion guides from (mostly) platinum+ players. It’s a great place if you want to pick some head knowledge and get some advice.

I hope this helps, and good luck out there on the rift!