Hi @ all!
This is my first Guide and i hope you´ll enjoy it.
I created this Guide, because Renekton is my favorite Champ on toplane
and i think you will have a lot of fun while playing him. :)

Renekton is really strong in early game, but if you don´t manage your
laningphase well, you will have problems to get back in the game.
I have to say that i play very aggressiv with Renekton, because his
abilities make him be like that and it´s really nice how well that works.

Effectiveness:

Early game > Late game
(Boss)_______(Okay)

I choose 21/9/0 masteries, because this makes you able to play very
aggressiv. The CD-reduction is cool, because you don´t use any mana
for your abilities. The rest helps you to do more damage instantly.
Barrier helps you while trading in earlygame and awesome lvl 3-5 towerdives.
I´ll explain that later. ;) Your Ignite also helps you to get the kill and
to counter heals like Volibears passiv or something like that.

The giants-belt or rather the Sunfirecape makes you really tanky and
synergieses very well with your ultimate. You will deal a lot of AoE-
damage in Teamfights and it´s also nice for farming and chasing enemies.
Take the shoes against your laner for wining your lane even more.
Blade of the ruined King: The lifesteal makes you a great dueller, also
with CD.
Spirit Visage is nice to boost your Q and lifesteal, the CD-reduction is
epic to spam your abilities and it gives you alot of nice MR.
Black Cleaver gives also some CD-reduction, life, AD and armorpen. Really
nice stuff for Off-Tanks ;)
As your last item you can pick something to counter the enemie team like Thornmail
or Maw of Malmoritus against fed AP-carrys; or you just buy some more health
for tankiness in general, like Warmorgs Armor.
When no more tank items needed, feel free to buy more AD stuff, such as Bloodthirster.

I like flat AD runes in Marks and Quints to have a big damage output from the
first minute of the game. I use instant Armor Seals to reduce minion, auto-hit
and tower damage, beause of these are the dangerous damageoutputs in earlie game.
My Glyphs are about scaling MR to don´t get ****ed up by roaming mid-laners in
mid-game. :D

In your laneing phase you´re able to use your full potential.
Renektons Q gives him a great sustain and farming possibilities,
while his E-W-Q-E-Combo is really epic for harassing. Befor u start
traiding, make sure that you have no CD, because Renekton really
needs his abilities for that.
If you get ganked, because your ward run out of time, or you haven´t
enougth gold left, stun one of the enemies(W) and use your E to jump
away, but make sure that you hit at least a minion to use it again
for super great escape.

Because of your super jump E you don´t really need flash, so we
picked Barrier. And because of we´re so awesome and strong in
earlie game we bought Elixier of Fortitude. Both is really im-
portant for the aggressive way we play the game. When your enemie
is lowlife, but you too, dont be afraid to start the fight. Use
the Elixier for the HP and AD boost, and if thats not enough use
Barrier as well.
With exactely this combo Elixier + Barrier you can towerdive at
low level. You will dominate the first minutes of the game, because
of your redpots and Q; so while traiding you and your enemie loose life
but you regenerate more. So when you are half-life and your enemie just
1/3 up to 1/4 life, the towerparty starts. Use your E to dive in, when
you have more than 50 Rage for the extra damage, activate Barrier + Elixier,
finish the enemie of with your W and Q, then go back with E again and your
done. This works pretty well, i often got first blood with this tactic.
NEVER FORTGET: Only do this when you have an active ward or know where the
enemie jungler is!!!

In late game, it´s a bit difficult what to do with Renekton. But going tanky
is a good decision any way. With Blade of the ruined King, Renekton is a nice
split-push and backdoor champ as well. In teamfights you should initiate with
your E in all five enemies and use R, what makes you even more tanky, and stun
the enemie ADC. Mostly you will work as a tank, but Renekton is also really strong
in 1v1 fights and you´re still able to deal some damage.

So I hope my Guide showed you a nice way to play Renekton on toplane,
and I would be glad, when you rate this guide and leave some comments,
what you think about it. Have a nice day and good luck while playing
League of Legends. :)