This is how I play Shaco, mainly in 3v3 matches. This build is VERY expensive, just over 20,000 gold cost, and 17000 IP for runes. I rarely complete it in 3v3 matches, but even not fully built, it destroys enemy champions, and I have yet to find a build for Shaco that works better for me. This build is all about critical hits and lifesteal, enough so that you can go head to head with warwick. This build also allows you to do decent jungling, so much so that you can easily solo baron by the end of a 5v5. Now, this is definitely NOT an AP build, and the closest to tank items are lifesteal. If you don't land hits, you will be helpless. You need to remember that running away may get you killed while staying, fighting, and lifestealing could keep you alive and possibly get you a kill.

EDIT: Changed out Executioner's Calling for Trinity Force, this way you still ge the crit chance to 100 but you get all those other nice little on hit effects, as well as a bit more move speed. The major thing is just the Sheen effect on trinity force combined with deceive. Full build means 150% of attacks damage * 2.67 on crit * 1.2 damage from behind. There's also the armor pen to add into that. I may actually figure that equation out at some point, but too lazy atm.

EDIT: Well, at lvl 18 with these runes, masteries, and items, base damage will be 294. The total damage from the deceive with everything added in (including attacking from behind) is 1413.06984. The lifesteal will heal you for 565.227936. Note, this is BEFORE armor AND armor pen. Those will drastically change the total amount.

First thing you may notice is the 8 items. This because you sell and replace two of them.
The order goes like this. At start, get boots and potions. As soon as possible, go back and upgrade to greaves. Next, get Wriggle's Lantern and Stark's Fervor. Once those two are done, you'll have decent life steal, so you can pick up your first phantom dancer and then the infinity edge. After IE, grab the Executioner's Calling. This is where your inventory fills up. Wait until you get enough gold to buy the next one as soon as you sell the old one, but trade the wriggle's for a Gunblade, and the greaves for a second phantom dancer.
By the end of this build, you have no boots, but 2 phantom dancers means you're still pretty fast. You will have 58% lifesteal and 25% spellvamp, so you'll heal yourself a lot in combat. You'll have 100% crit chance with masteries, and you crits will deal 267% of your base damage. Combined with armor pen, that is nothing to be ashamed of.

I chose these runes for 3 reasons. Armor Pen will greatly help you out, because it increases your damage, and therefore your lifesteal as well. Crit Damage is nice because by the end you'll have 100% crit chance and bonus crit damage, so you'll be constantly dealing out the hurt. Finally, I cannot count the times that deceive has either gotten me a kill or prevented the enemy one, so the cooldown reduction helps you use it more often, plus more cdr equals more clones. You can change the glyphs out for more critical damage if you like, but I would suggest sticking with the cdr.

Unlike most people, I put more than 21 points in offense. 25-0-5 May seem less balanced than 21-0-9, and it may very well be. I'll tell you when I start caring. I max out physical damage output and the cooldown reduction, but since this is not an AP Shaco, I ignore the magic pen. You can get it if you like, but I prefer the small exp boost. For summoner spells, I grab Ghost and Rally, and upgrade them both.
Ghost vs Flash: Flash is better for getting away immediately or catching up immediately, but Shaco already has a flash built into his deceive, and Ghost is more useful, because it lasts longer than flash does, so it takes longer to get short distance, but at long distance Ghost is faster.
Rally: I feel like rally is a severely underused spell. Think about it, Shaco has himself, his clone, his boxes, and his teammates. He benefits greatly from it. His AP is boosted so more box damage and clone explosion even in an AD build, and his and his clone's AD is boosted as well. Also, it will absorb a couple tower hits if need be. You can use it to help back door without a minion wave.

OK, everyone nowadays does a team fight in bottom lane at beginning of 3v3 matches, so grab your starting items and get there asap. The boots will help make sure you're one of the first. Go into the bush leading to the jungle closer to the enemy's base, and wait until your teammates initiate to pop in with deceive and use that mighty crit damage. Don't forget to use your summoner spells too, a Rally can really screw the other team over at level 1. Finally, try as hard as you can to get that first blood, because that'll give you enough gold to buy the dagger for your boots. You will want to get the solo lane in 3v3's as often as humanly possible. This way you will be able to level up faster, farm better, and gank more quickly. Remember to put your boxes in bushes to act as wards, and your wriggle's as well if you have it. Most importantly, don't stay in one place. Make your enemy lane partner spam his chat with mia's. Deceive into the jungles to grab buffs or to gank as much as you can, but try not to leave the enemy alone in your lane for too long. Finally, be aggressive, don't let your enemy dominate your lane. You need to make him realise that this is your lane, not his, and that just because he can't see you doesn't mean you can't slice his throat.

3v3 and 5v5 are two VERY different things to master. For 5v5 you may want to get Boots of Mobility instead of Berserker's Greaves (you'll still probably want to replace with phantom dancer anyway) so you can gank more quickly. Don't forget about jungling too. Getting Blue Buff will increase your box damage and clone explosion damage (which never hurts) and more importantly reduce your cooldowns. Red buff increases your on hit damage and apllies ANOTHER slow to each basic attack. Dragon is worth as much gold and experience as two champion kills, so grab it as much as possible. Finally, when the build is finished you can easily solo baron, just make sure you put boxes to warn of impending ganks. You will also need to be able to decide whether you'll be more useful in a team fight or knocking down a turret or two. AD Shaco is one of the best backdooring champions out there, so you need to make sure you use his talents well. However, if the enemy is pushing down an inhibitor and half your teammates are dead, you'll probably be more useful defending. You may also want to get Jack in the Box at level one to grab either blue or red buff as soon as it spawns, in this case change the skill sequence to Box at level one, Deceive at Level two and three, Two Shiv Poison at level 4, and then return to the normal sequence.

1: This guide is called the Ultimate Troll because to me, that is what Shaco is. His abilities are incredibly good for harassing, ganking, escaping, and just plain making the enemy champions mad. Knowing how and when to use these abilities makes you a force to be reckoned with.

2: I cannot tell you how many times I've seen bad Shacos not get kills because of mis-using the shiv ability. Yes, you can throw it and do a bit of damage and slow. However, if it isn't on cooldown, it applies the slow to EVERY HIT. It means you basically have a constant lizard buff if that's active. You should only throw the shiv if you are sure it will kill the target, and not even then if there are other enemy champions nearby. In order to be able kill, you need to be able to catch. Pop the hextech gunblade active use if you really think you need to use a ranged slow.

3: Use your clone strategically. Let's say you see Malzahar by himself in his lane. You can either deceive next to him, pop clones, wait until he targets the right you, and then nukes you with combo and bam your dead, or you can be smart. Hide in a bush nearby, then pop your clone. If you hold down alt and give commands (move here, attack this, etc) while your clone is active, it'll make the clone do it but not you. So, go into the bush, pop your clone, send him next to Malzahar who (9/10 times) will just see one Shaco, assume it's the real one, and then waste his abilities on it. As soon as he is on cooldown or the clone dies, whichever happens first, deceive next to him and kill him. This works especially well with Malzahar, but can be applied to nearly any champion (Annie's stun, Ryze's snare, WW's suppression, etc)

4: Use your abilities. All of them. Including the passive. Always try to land a deceive hit from behind for even more damage. Always use the passive effect on the shiv. Always use your boxes as wards and to help fight/run away. When laning, always try to hit minions (and enemy champions) from behind, that 20% bonus damage makes a big difference at level one. Also, don't be afraid to chase enemies back to their turrets, hitting them from behind while they run will hurt. However, never, ever, ever turret dive until you're at least level 10-11, no matter how low their health is.

5: Know when to fight, when to chase, when to defend, and when to get the **** out. Your lifesteal will keep you alive, but only if you can get close enough to actually start hitting the enemy. If you're snared/stunned/suppressed, you can have 5000000% lifesteal and it won't help a damned bit. Trick enemies into wasting crowd control on your clone, as told in tip 3. Also, Tryndamere on undying rage with no health means no damage which means no lifesteal. Don't stick around, back out of range but keep close enough to finish him off when it ends. Also, Jax/Sivir/Nidalee/other dodge stat champions can be a huge problem. If you're fighting one of those champs who is building dodge, then grab a Sword of the Divine instead of Executioner's Calling, and don't forget to use the item effects. Finally, Blinds like Teemo's dart or Heimerdinger's grenade can be extremely annoying, so don't think you can just lifesteal your health back if you're blinded.

6: Don't take unnecessary hits. When you're jungling, dropping a box or using the clone will sometimes result in the monster still targeting you. Right after the clone/box starts attacking, deceieve to across the enemy from the clone/box. Wait until they turn to attack them, and then you'll be behind them, for extra damage. This way you'll do more damage, take no damage, and get a chance to lifesteal back some health if you're losing more than you're healing. This is not for fighting champions, this is for fighting neutral monsters. Never waste your deceive in the middle of a champion fight unless you need to for the kill. Always try to save it so you can escape if you need to.

7: Backdoor, Backdoor, and Backdoor some more! AD Shaco is an incredible champion to back door with. He can drop wriggle's ward (if you still have the item), box, rally, and clone when fighting a turret. All of these will take turret aggro before you (unless you hit a champion) and they all have other uses. Clone will hit the turret, Rally will boost damage against turret, boxes will fear minion waves and hit either them or the turret. Well placed wards will still absorb turret hits while they still provide sight. The major thing you need to remember, however, never backdoor when you can't deceive away. Always have your finger ready to deceive as soon as you see an enemy champion, even if the turret only has 1 hp left. Letting them snare/stun/suppress you could very well mean death, possibly without even getting the turret kill.