I go with 9/21/0 build. Focusing more on physical reduction. Why? Pretty much all carry are physical damage dealers, and tbh thiese are the most threating targets and your team should be focusing fire on them.
Ardor scales nicely with your Seismic Shard. Bonus HP is crucial on early game while you soak the abilities with your Granite Shield.
9 in offense can be swapped for 9 in utility until mastered Clarity.
I like going 9 in offense for additional magic penetration since most of the damage you will deal is magical, and you want to deal damage so the enemy team cant ignore you totally.

Granite Shield - Malphite is shielded by a layer of rock which absorbs damage up to 10% of his maximum health. If Malphite has not been hit for 10 seconds, this effect recharges.

This is one of the most annoying passives ingame during early game. At lvl 1 you have 800HP (+82 per lvl) so your shield blocks up to 70 damage!
This might sound low but every 10 sec you have another 70HP. So you can take on your face a Gankplank parrrley, veigar balefull, Ryze flux and many many more, without even taking any damage! When your shield is destroyed, just back up a bit for 10 sec and recharge it than go again and harras/lasthit or soak spells for your lane partner.
Later on this becomes marginal but it is still valid to "eat up" plenty damage while getting golem buff or killing dragon.
The damage soak is calculated AFTER armor/magic-resist.

Seismic Shard - Using his primal elemental magic, Malphite sends a shard of the earth through the ground at his foe, dealing damage upon impact and stealing movement speed for 6 seconds.
Deals 80/135/190/245/300 (+0.6) magic damage and steals 10/15/20/25/30% movement speed from the target for 5 seconds.

Cooldown - 12/12/12/12/12 seconds
Cost - 80/90/100/110/120 Mana
Range - 700

This is one of the most versitale spells ingame. Great for harras since damage is quite high. But main use of this is to slow down enemy while speeding you up. I use it in my combo on teamfights, this requires Vent/TS/Skype communication or pinging. You pick up your target from the group (main target should always be the main carry of their team), you charge in, slam, pop-up the Brutal Strikes and you call witch target you slow. The moment that carry notices he is beeing targeted he/she should run away, but he/she is already low on HP due to your ulti-slam+melee hit with BS active, so shard will make him just "try running away".
If you feel unsafe or you see one of the misses going for you quicky use shard and sprint away (you might use your flash to be even further).
In chasing scenario, you can slow down the enemy while speeding yourself, its also vital to flash-shard enemies that try to run away.
Remember to use it while killing the golem. The mana cost will be replenished pretty fast anyway.

Brutal Strikes - Malphite hits with such excessive force he deals damage to units around his target. He can also call upon his strength to increase the damage he does for a short time.
Passive: Malphite's attacks hit units near his target for 30/35/40/45/50% of his attack damage.

Active: Malphite hits for 30/40/50/60/70% more damage for 6 seconds.

Cooldown - 20/20/20/20/20 seconds
Cost - 55/60/65/70/75 Mana
Range - 400

This is your DPS tool. Getting this on lvl 4 will make your farming easier and you will already have full combo on lvl 6. (450 damage total + your brutal strike melee damage)
In early game swap targets while meleeing and finish off with Slam killing whole pack in no time, just watch your mana pool :).
On Tank build this is more for farming and a little bit of damage boost, this is why we max it out last.

Ground Slam - Malphite slams the ground sending out a shockwave that deals base damage plus half his armor as damage and reduces the attack speed of enemies for 4 seconds.
Malphite slams the ground dealing 60/100/140/180/220 (+70% of his Armor) magic damage to surrounding enemies, reducing their attack speed by 30/35/40/45/50% for 4 seconds.

Cooldown - 8/8/8/8/8 seconds
Cost - 60/70/80/90/100 Mana
Range - 300

This is what makes you lethal to enemy carries. A good lategame ulti-slam combo will take more or less 700-1000 damage. Also it is undodgeable for all that got cought by your ulti, they are simply damaged in mid-air. Reducing AS by 50% is crazy boost to your survivability. A little bit math, lets take Yi as example. Usualy you have Yi with 2.0 AS, and about 300 AD. His damage output is equal to 600dps. A slam makes it cut to half. The diference is HUGE. Its like you "disable" 2AS/AD items in 1 button. And this math ignores Armor.
This is also the reason why you stack up on armor even if your oposing team has 3 casters.

Unstoppable Force - Malphite ferociously charges to a location, damaging enemies and knocking them into the air.
Malphite charges towards the target area, dealing 200/300/400 (+1) magic damage and knocking enemies into the air for 1.5/1.75/2 seconds.

Cooldown - 140/125/110 seconds
Cost - 100/100/100 Mana
Range - 1,000

Pros:
- Great initiator
- Superb physical damage tanker
- Good chase/escape mechanism
- Great AoE creep farmer
- SUPERB early game skill soaker
- Good harraser
- AWESOME burst capability


Cons:
- Item dependant
- Diferent skills scale with diferent stats
- Needs a "thinking" team that will not waste your ulti+slam combo to work good.
- VERY VERY Mana dependant and unefficient