This is a guide for a fun interesting build of Malphite to catch people off guard and beat their faces in. The idea of the build it to make Malphite an ad bruiser and abuse his Brutal Strikes to deal massive damage. The build gives Malphite plenty of tankiness, sustain and damage.

Fairly basic ruin set up. Trying to make an ad bruiser so take the attack damage marks, and attack speed quints for damage, and for tank armor seals and scaling magic resist gylphs

Core:
Ravenous Hydra: the best item to get for almost any ad bruiser , gives sustain and aoe damage to auto attacks.
Frozen Mallet: Another great item for Malphite, gives him tankiness with a little bit of extra damage. Main use of the item is for the passive to keep enemy champions from running away.
Last Whisper: extremely useful item gets around a good chunk of armor and gives damage to boot.
Attack speed:
Trinity Force: my preferred item to help increase the attack speed of malphite, gives lots of useful stats and the passive help increase damage output by a lot.
Blade of the Ruined King: another option for increasing attack speed, gives some additional damage, nice for the lifesteal and active to make it harder for enemy champions to get away.
Magic resist:
Maw of Malmortius: preferred item for magic resist and attack damage on malphite, both passives are very nice.
Mercurial Scimitar: other option of magic resist, usually only get if enemy team has a lot of cc.
Boots:
Ninja Tabi: nice way to round out the build since there is a lack of armor in the build.
Berserker's Greaves: nice for the additional attack speed.
Mercury's Treads: tenacity is always nice and gives additional magic resist if needed.

Seismic Shard you get level one in order to have poke in lane, this skill gets leveled up second mainly for the increased slow, but also the extra poke damage.
Brutal Strikes you get level two for the AOE from passive and the buffs from active, this skill gets maxed first as the buff is the entire reason for the build.
Ground Slam you get level three for the additional AOE, this gets maxed last but still offers a nice debuff with reducing attack speed.
Unstoppable Force you level up when you can, its the main way of initiating a fight and offers nice cc if used correctly.

Flash offers too much utility not to take as one of your summoners.
As for the other it can be anything you like, I prefer Teleport since Malphite can be slow to lane and offers map pressure being able to Teleport anywhere.

The whole point of this build is to abuse Malphite's Brutal Strikes skill to increase his attack damage by 40% once fully leveled. Using the full build as an example, at level 18 you end up with over 350 ad, with the 40% boost you when you use your skill end up with over 500, that then procs Trinity Force allowing you auto attack to deal an additional 200 damage. The final build gives Malphite over 3000 hp and 125 armor and magic resist allowing him to continue to tank for the team if needed.
The other great combo with Malphite is with Brutal Strikes Passive, and the Ravenous Hydra, these allow for a lot of AOE from auto attacking meaning if you Unstoppable Force into the middle of the enemy team and start punching you're doing massive damage to everyone.