A Lulu build with enough AP damage output for harass and enough mana/CDR for continuous quick casting of abilities for the best crowd control. Great survivability too!
Just like Lulu, this guide is short and sweet, so have a quick read to get the most out of this guide!

Pros

• Abilities that will annoy the enemy so much.
• A champion you can be extra creative with (moving Pix around and also being a very subtle CC)
• Gets unexpectedly tanky mid-end game

Cons

• Moderately squishy and slow only early game. (However this build will make her tougher than you can imagine)
• Not the best damage unless you build her as an AP carry. However, she can harass quite well, especially early game and she is an incredible asset to any team having so much utility value! Definitely can clean up well.

My skill sequence outlined above is NOT set in stone. Be flexible! Feel free to get Whimsy before Help, Pix! if you need to suppress a strong pushing enemy in a lane more than harass/damage. However, the reason I get Help, Pix! before Whimsy is that it can actually help you harass and push back! It allows you to move Pix to a minion or champion (ally OR enemy). Once, Pix is in position, use Glitterlance to shoot from two locations! You can get quite creative with this, giving you some extra range or hitting several champions at once.

Why do I max Help, Pix! first?
This guide uses Lulu mostly for her utility value. That is, Glitterlance is used for slowing the enemy and Whimsy is used for the enemy silence/slow or ally movement speed increase. By maxing Help, Pix! first, you have an ability that can give your ally an intimidating shield as well as some decent burst damage if used on an enemy.

So I've explained the unique game play of using the Help, Pix! and Glitterlance combo during laning. It can be used in multiple situations, such as in chases. That Ashe is getting away? Use Help, Pix! on the ally chasing, then Whimsy for the speed boost and finally get a Glitterlance hit on that Ashe from the Pix flying on your ally to slow her down. Remember, though, that you still need to be vaguely in range of the chase as well to shoot Glitterlance from Pix.

Some other tips that you would probably figure out if you played Lulu a few times:

• Remember that Whimsy is great for suppressing any area of effect abilities such as Defile, Crowstorm, Bullet Time, etc. Maybe even more useful, especially for escaping or during laning, you can prevent any abilities like Fling or Thundering Smash that can get you into some sticky situations.
  
• A combination of Wild Growth and Help, Pix! on a single ally will make them live for SO much longer whilst also giving your team several kills in a team fight.

Some optional items that are useful:

Nashor's Tooth
AP, Mana Regen and CDR are all super useful

Shurelya's Reverie
If you need an extra health boost/health regen + CDR. Active is also great for team battles/pushes.

Soul Shroud
Great health boost with mana regen and a little CDR

Other items to support your team (mostly for late game) include:
Zeke's herald
Judge which ones will benefit your allies the most.

and to help in team fights:

If something like Idol of Durand happens, you can deflect it and quickly use Whimsy on Galio to save your allies.


When upgrading from your Boots, make a judgement of the game so far and who will be giving you/your team the most trouble. I usually get the Mercury's Treads for the magic resist against any enemy AP with burst damage that may try to target you. I find AP give me much more trouble than AD. Plus who doesn't love that Tenacity? However, Ninja Tabi and Ionian Boots of Lucidity are also decent choices. Although, with the item sequence I've suggested, the CDR given by the Ionian Boots of Lucidity can become slightly obsolete. If you need that CDR early on in the game though, it is a good item to get but be prepared to change some of the other items that give you CDR since you may begin wasting your gold when you've maxed your CDR already! Mobility Boots or Boots of Swiftness aren't too bad either.
Don't even think about Sorcerer's Shoes, this isn't an AP carry build.

Get wards whenever your team is seeming to be blind and the enemy team is dominating the field. This means you'll need to have an item slot available as much as possible. Remember, you can probably sell your Doran's Ring in the mid game, any time after you have your Rod of Ages.

Choose Heal or Clarity based on who you are laning with.

Teleport is great for mobility to get you to those team fights ASAP or getting you to turrets being overrun by minions. Ghost is also an option instead of this but you may need to also rethink your boot choice.

Nonos:
Clairvoyance is optional but wards are a better option.
Haven't used Flash as Lulu and don't see how it would help.

Farm normally, don't hog it too much. Try not to get too many of the kills unless you must, you definitely want your carries getting the kills. Assists and a moderate farm should get you the gold you need for the build.

Be in EVERY team fight!

YOU are responsible for wards! Try leave an item slot open to keep wards.

Thanks for reading! Hope you enjoy using this guide.
First guide here so please leave comments about what you like or dislike =D
Peace.