If you're looking for a powerhouse tank that refuses to die while killing carries and just generally eating face, look no farther. not to mention your an 8 foot walking iron man.

sorry for the lack of proper capitalization, punctuation, grammar, ect. This is a good build for beginners to look for easy skill and item build.

Pros:
Passive is one of best in game
Creeping death is great for harass and carry shielding
Awesome farmer
Packs an impressive ap punch mid to late game
Lord Mord is best skin in game

Cons:
No cc to speak of
Will cause opponents to flood chat with their cries

Ghost and Ignite are the only real spells to use.
Ghost lets you stay with the enemy with your creeping death and makes up for a bit of your lack of cc.
Ignite simply because that plus your a well placed ult will net an almost guaranteed kill.

Children of the Grave > Creeping death >Siphon of Destruction > Ace of Spades

use Q W E on cd and don't be afraid to use your ult on someone just to get health back. i always open with ignite when i get to lane because of the bonus mastery ability power and it puts you in a strong position. if you get harassed hard in early game, use Creeping Death to safely harass and get some minion kills by putting it on a friendly melee creep. max it first because you are ultimately a tank and it gives the best harass and survivability for you. abuse the **** out of this spell. use it on carries (especially melee carries) for more damage output and give them more survivability.

Q is my least favorite spell because its the only of your first three that isn't a total aoe and it does less damage overall. it starts to shine late game when you hit solo enemies for the bonus damage.

after you get to level 4 or so, feel free to get some free gold and exp from the jungle. your hp5 and passive make it pretty easy. a fed mord is usually a good game

my build is this 90% of the time.
Force of nature > boots > warmogs > rylai's crystal scepter
by this point, you should be able to walk wherever you want and do good damage too.
late game, deathcap makes your ult do dumb damage and your last slot is either lich bane (it will always be up and you have good ap to make it hit hard) or banshies veil for ap heavy teams or thornmail for those heavy ad teams (love to watch champs kill themselves)

force of nature, boots, crystal scepter, and lich bane all help your one core weakness: lack of cc.

offense tree should be pretty self-explanatory. ap, spell pen, cd reduction, and more ap is all good.

defense is the deepest tree we use because we are a tank and we get the most use out of it. armor, magic resistance, dodge and move speed on proc, more armor (basically), health, and ability power. all good stuff

ghost is the only thing to take out of utility. getting down to exp gain increase is viable but you lose a lot of good things from defense if you decide to do that.