Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Looked up a build for Mordekaiser and decided to combine an item order for a rammusbuild with Mordekaiser. Tried it out a couple of times and it hasn't failed me yet.
Mordekaiser original build: http://www.mobafire.com/league-of-legends/build/mordekaiser-the-hellknight-1886
Rammus original build: http://www.mobafire.com/league-of-legends/build/rammus-killer-852