This build centers around, as you guessed: Renekton, who is a surprisingly strong hero from what I've played. This is my first build, and I'm only a level 8 at the moment, so please be gentle.

Armor penetration: Just to make getting through what little armor they will have left even sweeter.
Cooldown Reduction: Great for being able to spam all your skills more often, no mana, no energy, Spam away!
Armor and Magic Resist: For that little bit of extra survivability everybody loves to have.

Experience: An overlooked Quint from what I've seen on most builds, it gives a grand total of 11% extra experience with your Masteries, and should you get a Zilean on your team, it pops it up to 19%. Imagine, leveling almost 20% faster then your allies and enemies!

I chose a mixture of damage and the support tree. This build is centered around doing a lot of damage with his skills, making the cooldown reduction very handy for his no-cost spells. The attack speed helps and should give you almost 2.0 Attack speed by the time you finish your Black Cleaver, while armor reduction builds very nicely with the -armor items I've selected for this particular build. The health regeneration and experience help you keep in the lane longer, but you get 11% extra XP total with your Quints.

I like to get heal as that last second "Panic" button to save yourself or a team-mate that's running from a horde of angry enemy Champions, though Ghost also helps with this, it can be used to get the jump on enemies and keep up with them early-mid game.

Cull the Meek: Excellent for keeping you in the lane longer early-game, and will be your main farm skill mid-late game
Ruthless Predator: Your Primary killer, with 50 Fury it hits three times (With On-hit effects) and stuns for 1.5 Seconds
Slice and Dice: A great farming skill, also VERY usefull for when you're chasing a pesky hero, can jump into them twice as they cower!
Dominus: +HP, and a wicked AoE damage, great for team-fights, that little extra HP for escapes, and for chasing heros you wouldn't be able to kill without its aoe damage.

I like to start with the cloth armor first to get that little bit of extra armor in the beginning, the health pots increase your laning ability if your harassed a lot, or try to make a lot of early-game kills. When you get enough gold, hop over to get the Madreds, and boots if you can afford it. When you have enough to finish up your attack speed boots, hit the jungle until you can afford the emblem. From there I like to hop between lanes, the jungle, and gank until I can afford the Recurve bow, then I build fully into the Madreds. The primary reasoning for getting Madreds, is it stacks VERY well with your W skill. With 50 fury it strikes three times while applying on-hit effects, (12% of their HP From Madreds, then soon -45 Armor from cleaver). From there, more attack speed with the bow to build into your Starks for a -20 Armor aura, and some very pleasant attack speed and Lifesteal. Black Cleaver adds in some necessary direct damage to bolster your abilities, and lowers enemies armor with ample spammage of the W key. The next item, the Mallet, is to prevent those DPS enemies from running away (Should they be able to get past your E) and provides you with 700 HP. The final item is up to you, I suggested Infinity Edge for its damage and critical strikes, with combines well with your 1.8 Attack speed, though you may want to consider a survivability item, such as Magic Resist, or a Thornmail. My final suggestion, is if you're fighting a high-armor character, (Rammus, Shen, ect.) Last Whisper, for the added 40% armor penetration on top of your -65 total from Starks and Cleaver.

Excellent at 1v1 fighting and can be a great morale weapon against the opposing team.

Very High damage in a short period of time
Above-average Survivability
Above-average in Team Fights
Great farmer with W and E

Please comment! I'm always open to suggestions on how to improve it.