Masteries
Items
Skill sequence
Summoner Spells

I take defensive masteries because, well.... he's a tank. this wil give you easier laning and survivability. and you have spell penentration and ap early giving you an easier early game.

Doran's shield
First get Doran's shield for health regen and armor.

Boots
Ninja tabi or mecury's trheads depending on who is fed. (ap or ad carry)

Warmogs
Get warmog's early so that you stack faster. Warmog's is a given for tanks. it gives tons of health and it stacks with malphite's shield passive.

Frozen heart
Frozen heart is godly good with malphite. it gives him tons of armor, very much needed mana and insanely good cdr. the only thing that might drag it down is the enemy aura. This makes it harder to ambush or gank.

Tiamat
Now many may ask like WTF TIAMAT. tiamat stacks with malph's w and gives him precious health regen.it also gives ad to add to his low dmg output.

Atma's impaler
By this time of the game, i am usually finished. You should have alot of health by now so this is a good choice. also it gives armor and crit.

Force of nature
you may want to get this earlier if they have an insane nuker. it gives health regen, so it allowes you to stay longer in lane. it gives move speed which is one of malph's great weaknesses. also it makes up for the lack of mgc resist in thisd build

You might want to switch this build a little as the game goes. always by situationally items.
P.S. Health is the greatest defense, it defends against true phys and mgc dmg.

max q first! that way you can chase more easily. also it deals substantially dmg early.

after comes e. this is to further dmg output and to make use of the armor tank.

W last. i dont consider w to be a good spell it is good for laning but not much else maybe for getting away or quicly finishing a target.

In battle. Rush in with R, immideatly activate W then E. this gives you the armor bonus from W to dmg in E. also you dont die as fast. save Q for harrasing and chasing if they try to escape.

escaping. use q to slow them, ult to get away or "stun" them, or w to get armor bonus so you dont die.

I take ghost and ignite. i reccomend these spells for chasing and damaging.

other acceptable spells:

Exhaust
Flash
Heal
Teleport