Well.....Lulu was Just released and I have tried about 3 builds....and this one....well. It's ghastly. Lulu becomes a veritable force to be reckoned with. Try it and tell me what you think. Constructive crits appreciated as this is my first build.

Okay, so... for runes I chose attack speed g/5 and ability power.
I chose these because attack speed takes advantage of her passive and with the slow from T-force you have yet another form of CC on this champ...which is prolly overkill but man is it fun. G/5 because this is a terribly expensive build. Rarely do I see then end of it though. Ability power/ level, she's an ap champ and that ability power can translate into more tankyness or more damage output depending on spell cast (friend/foe)

For my masteries I built to increase tankyness and gold generation through assists working towards some cd reduction and spell pen. This helps you get through your build faster, gives you a bit of staying power and adds much needed spell pen for this build. primarily your role will be messing with your enemy team though, so spell pen is not as important in the damage dept.

Okay so I open with the Reqrowth pendant and a health pot. (Lane presence)
turn the regrowth pendant to a philo stone. (think about buying some wards)
buy your first level of boot next and work towards a catalyst. (With your gold generation this should be pretty quick)
I then go back for my ionian boots and a blasting wand (sp and cd reduction should be self explanatory)
finish off your rod and then head into the Rylai's (now you are starting to get pretty tanky and have become AMAZING at initiation, a poly that has a 35%+ move speed reduction is OP)
Build sunfire (more damage and hp stick to your enemies like glue and watch em burn)
From here take creative licence, if their team is heavy hp think about mr ad...try a thornmail this is where I often abandon the rest of the build for other items as needed. If you are getting fed the last two just add extra OOMPH.
Nashor's Tooth is also amazing on her.

Why Ghost and heal?
Ghost is pretty decent Flash could be more preferable but i find giving my self a spell speed buff + ghost means i can get anywhere quick and my spells often get me out when i need to.
Heal....while often dubbed a noob spell it's the only thing this champ is missing as a support champ and while tanky people only complain when they are dead and you aren't.
And if winning is not worth being called a noob....pick something else. But I mean it when I say Heal rounds out her support the way nukes round out an army.

I have not finished skill order yet but I want to play some more and I will finish it soon.