Malphite Is Not A Tank, why? Well though he is pretty tough he lacks tanking skills, no self heal, no healing on kills, no passive armor-to-damage, etc... even though he has a passive shield, that's situational. I hardly ever see anyone playing Malphite and the builds here are a scarce few, so i decided to add my own.
Well you'll notice the item build has a few extra items, well there's never a formula, there's not a build that will work always perfectly in every situation, the thing is, everything is situational, if this was all about following a formula and win, we wouldn't be playing it, would we? the one with the best formula wins, hell if your opponents are really weak you don't even need to worry about skills, runes, items or masteries, so hell, always do as you see fit.
The items in here, are just a sketchy line, use them or not. I'll list them here by a random order, just stating their relevance.
The catalyst, good for giving you some health and mana for harassing lane opponents and regain some when you lvl up at early lane skirmishes.
The Hearts of Gold AKA Turtle shells well, optional, provide a bit of armor and a steadier gold income, which is always handy, it's totally optional though. Obviously sell them later for the high-grade items. (and the catalyst unless you get banshee's veil)
The Frozen Heart helps making malphite more of a fierce fighter, harder to put down, as well as slowing enemies a bit when it comes to answering your ultimate.
The boots of mobility, i personally like them, feel free to use any others though. (if you use the teleport summoner spell you don't need them as much, i use exhaust and ignite cause it helps scoring a few kills if well used).
A. The Bloodthirster, Starks Fervor, for damage speed and lifesteal.
B. Banshee's Veil, Force Of Nature, well if you got some serious spellcasters as enemies, go for those.
C. Infinity's Edge and The Black Cleaver, for raw damage.
From those 3 sets, choose 2, or just reinforce one of them, if your team has the upper hand in mid-late game you'll want speed and damage as you'll be (yes) hunting down people, exhaust, boots of mobility, and Seismic shard are... well great tools if you are chasing a lost lamb. (beware traps and ganking though)
Always remember, your passive shield can take some serious damage sometimes but it won't save your sorry butt if you get careless. Careful with stuns snares etc, or get Cleanse instead.
Hope this isn't totally useless, as this is just a fun way to play Malphite opposed to a tank role, have fun.