Renekton is a tanky dps melee character.
He is one of teh greatest offtanks in season one.
If you have played nasus, it will prbly raise your skills by 10%.
His Ultimate makes him verry durable in team fights but also at solo laning or while being ganked.

For renekton i take Arm penetration marks, dodge seals and cooldown glyphs. And i take 3x arm. penetration quintessences.
Why Penetration
You will get armor and magic resist itmes, so there's no need for marks like that.
Also he's dps tank, so it's verry usefull to get armor penetration so you can do higher dmg.
Why dodge?
Dodge runes are verry important not just for early but even for mid and late game. They can save your life many many times! RESPECT DODGE RUNES!
Why cooldown?
Well, if you have tried renekton before, you might have noticed, that his skills have high cooldown. His base attack speed isn't that great. Thats why you need CD so you can spam your spells on them!

For Renekton i prefer 22/0/8 masteries, cuz we'll get defense ingame.
instead of going 21/0/9 i take one point from utility and add it to ignite.
For utility i need only moving speed, exp generation and improved ghost.
Also tahts why i take 22/0/8;) to have improved spells. And you'll lvl up faster if you're solo laning.

For the start i takeand 5. Most of you would take Dorians shield. But renekton has Q spell which allows him to "lifesteal" from creeps. Also you'll have 5 potions, they should make sure that you survive(not if you're a noob).
After backing i getand.
Now that you haveyou should get gold faster so you can get next item as soon as possible. Next item should be.
Now, depending on your enemy, start of withor. Then head for the other item to complete your.
After you have some Armor, now it's time to get some Magic resist. Start of withand then purchase 2x. After you have these items, complete your.
Now your armor and magic resist should be balanced well. So take off and get some health for survive! Get(it gives you hp and dmg) and after that. So, now that you ahve both items, proceed to. It will give you even more hp and you'll be able to slow enemies down.
Allright, it should be around mid game now, where you occur in many team fights. So, get anotheragsint enem abilites and after that getfor more HP. If you have both items, you can get your. Allright, I've never got to this point before, cuz im too amazing to finish it before it even starts to be fun.
BUT!
If it happens to be your case, sell yourand getinstead. It's verry awesome! Not that it gives you armor, but it even gives you dmg which is converted from 2% of your hp! Youll have 200dmg+ about 170 Armor and 170mag resist. Now if thats not cool then i dunno.

Q spell
Good for farming creeps and regenerating your hp, allthought he hp regen isn't that high. But, thats why you have Force of nature.
W spell
Important spell you have. It deals superb dmg and it can even stun enemies, which will allow you to kill them easier or run away from 1v1.
E spell
Well i dunno..good for farming, running away, or chasing enemies. But..the dmg is like..ridiculous.
R spell
Verry usefull in teamfights, 1v1, or escaping. R spells summons a weird something around you which deals dmg to the enemies. Combined with your sunfire it's verry deadly.
Also it raises your hp by about 400points, which will save your life and make you mroe durable. Also it will automaticly refill your "rage bar" which will help you to deal more dmg with your spells.

Ghost
i think that's like the best spell you can choose for renekton. Ghost will allow you to run away from battles, or chase down an enemy and finish it off.
Ignite
You may get exhaust instead of ignite, but i prefer ignite, so if your enemy runs away, you'll be still in range to ignite your enemy and if your enemy is low on hp, you might kill him.

Renekton sure is a great G-farmer. From beginning on, you can farm creeps by hitting them with Q which will deal dmg to all enemies around you.
After you get sunfire cape, it will be alot easier for oyu to farm. Use Q-E combo for creep farming, the sunfire will do the rest for you.
Also your heart of gold will grant you some extra cash, which will help you to complete your build faster.

-Pros-
High hp
High mag resist
High armor
OK dmg
Great farmer
Great CC
Great ganker/pusher
Great in team fights
-Cons-
Hard to play
Hard early game
High Cd(get blue buff to solve problem)
thats all..renekton is a pro char.. xD no more cons:D