I've been playing Shaco for some time now, and currently is my most frequented champion. Originally I had played him standard AD jungler, and did fine. However, I've found that playing AP is just so much more delicious. We'll be focusing mainly on ganking with boxes, and somewhat little with shiv. Though in the end, shiv will be a decent nuke with some AP. Take a look at this video before you read the guide, for a proof of concept.

http://www.youtube.com/watch?v=c0_5CSnUWDM

Refer to the video that is posted above. I will try to, in plain text, explain my route under a preferable circumstance.

Start:
Counter Jungling. This is your bread and butter.

Your main goal is to deny their jungler of all buffs, and ability to gank.

Start off by grabbing your blue buff, if you do not have a jungler. Do so by stacking boxes before blue spawns, and then pulling the golem into them. Finish up the small ones for level 2, making sure to take shiv, and head to your opponent's wraiths.

Begin to stack boxes inside the bush, as fast as possible, and wait for him to approach.

As usual, he shows up with half to 3/4 of his health, and runs into the bush.
Wait for him to proc the JITB fear, then shiv, ignite, and melee attack.

First blood.

Typically, you will then stack boxes in the same exact bush, where you killed the jungler previously, and wait for him to come back. In most cases they will go directly through the bush the same way, to wraiths. If you don't think they will, or get tired of waiting, start stacking boxes by their red buff. If he goes to lane and won't hit your boxes, just take red and go lane as well.

Mid game:
At this point you need to level.

Typically what I will do is deceive from bush to bush in a lane, and stack boxes without them knowing I'm there. I will leech EXP and literally never come out, until they unknowningly walk in and give me a kill. If this happens, switch lanes and do it again. If they never come in, bait them.

If you prefer to farm, you can do so as well, though I prefer to do as stated above. Boxes are a great source for damage and will earn you some minion kills.

By level 9, you need to start doing roaming ganks. Setting traps in anticipation of ganks from other lanes, setting up traps and baiting/waiting, or just ganking with your clone and shiv, the old fashioned way. Your DFG should be complete by now, and will be an essential component.

Late game:
Pray you don't get here.
When playing AP shaco, you want to be SUCH a ****, and get so fed, that they're waiting for the 20 minute surrender. Late game, you drop off. Hard. The only saving grace is that you can pick off one or two with box traps before a fight. If you've been fed enough, you can typically take out their hardest carry, at the sacrifice of yourself, or if you time it right, can typically escape. Deceive in with an opening DFG, Lich bane proc, shiv, lich bane proc, ignite, clone, and then hope. I find this to be worth it, since you really have no part in group fights.

Should you jump in and attack someone as such, you will be targeted quickly. If you manage to escape, don't go back just yet. Start to stack in bushes behind them if they try and go around, or try and run from teammates. Odds are you will kill anyone who comes in before taking any damage.

I choose Magic Pen over flat AP without hesitation. The ratios on your boxes are 25% of your AP.
Therefore, as I will mention frequently throughout the guide, we want to focus on stacking Magic Pen to compensate. The same thought is applied to quints. You don't need health or defense for quints/seals because they're never going to hit you. Seals I go for CDR combined with CDR from items, you'll have all you need to maximize box stacking.

Same concept as for runes. Focusing on magic pen under offense, mana regen/cdr/buff durations. Buff durations are extremely important, as you will typically start at blue, and obtain many buffs from ganking their jungler.

Doran's ring first. This will give you just enough MP5 combined with masteries and runes, to stack boxes early in the game. I always pick up the pen boots next. This gives you extra mobility, but most importantly that 20 magic pen. You could theoretically get the Fiendish Codex first for the cdr/mp5/AP. However, as previously stated, I love Magic Pen for the boxes. DFG is an essential part of your build. It helps you to be useful in fights without using boxes. You also can use it just before an opponent walks into your JITB traps, for a guarantee'd kill. I get haunting guise for yet more AP, and then Deathcap. Lich Bane is also very essential once the game switches to team fights. You can deceive in, use your DFG, lich bane hit, shiv, lich bane hit, ignite, etc.

This is set in stone. As AP, you don't need the slow from shiv, so there is no point in maxing it. Each level from JITB gives you +20 damage. You would need 80 AP to match that. Since you will be focusing on JITBs for the duration of the game, it's common sense that you need this maxed first.

Ignite will be needed to pick up the early ganks. I take flash always. Having a double flash is insanely useful. It will also be essential at level 1-3 to escape if a gank goes bad, since you will not have deceive yet.

Pros:
Sets the best traps. Period.
Shuts down enemy junglers completely.
Very good K/D ratios.
Enemy is afraid to go into their jungle/bushes.
Enemy will not chase you or your teammates into bushes.
You can easily kite melee champs with boxes.
Provides escape routes in group fights.
Everyone will love you if you succeed.

Cons:
Tough to play.
Can be a very hit or miss build.
Teammates will hate you if you fail.
Potential to become very under-leveled.
Late game drop-off if no early game kills.

I always start off at our blue if we do not have a jungler.
If you have a jungler on your team, and they don't: start on their blue and then go to lane.
If you have a jungler, and so do they: If the opponent starts at blue, gank him above wraiths.
If the opponent starts at small golems/red: Steal their blue and gank him at blue.

Going back to traps.

You can use them defensively.
Protecting Allies:
Set up boxes in a bush that your enemy will use to gank a lane.
Set up traps in areas that can also be used as escape paths for allies.
Using Deceive on top of enemies and using your clone is a good way to scare enemies off.

Offensive:
Get teammates to bait other into your boxes.
While setting up traps, always be aware of your surroundings. Be prepared to help allies pick up kills. (Also known as KSing.)

Once a tower is destroyed, you should go to that lane. Stack boxes in a bush where the opponent will potentially gank you. Then proceed to farm the minions in that lane, while keeping your trap full of boxes. What typically will happen is that they will either; Let you free farm, or try and gank you, resulting in their death when they find your trap.

Probably the most fun I've ever had from League of Legends comes from this build. It is easy to get first blood and early kills, but the laning phase is tough to master. If nothing else, you should be able to get quite a few laughs at the expense of others.