Welcome to my Lulu's build ! I'm Inyri from EUW, I'm top ELO ( I don't really like solo/duo queue, I prefer playing for fun with friends in normal games ), and I wanted to share my Lulu's build here, because I always read guides on mobafire before playing a champion. I'm sorry if it's not really clear, english isn't my native language and this is my first build.

Pros
-Awesome snare
-Really good damage early-mid game
-A 2sec crowd control
-A good shield
-Movement speed buff
-She is a yordle !

Cons :
-She can't heal
-Difficult to master
-Squishy early game ( but which support isn't squishy early game ?)
-She is a yordle...

First of all, start with Faerie Charm, one pink ward ( Why ? To destroy the other ward, but take care of ganks, you're really vulnerable when you destroy it ), one green ward, one health pot ( Lulu can't heal :( ) and one mana pot ( Lulu has some mana problems early game ) .
Then I go for Philosopher's Stone, which is perfect for her ( health/mana regen, gp5 ), boots and wards again.
After that take Heart of Gold ( more HP, more survivability, more gp5 ) and if you can, buy Ionan Boots ( This CDR will help you so much early game ) .
More CDR with a Kindlegem, and use it for a Shurelya's Battlesong.
After that take basic support items ( Aegis of the Legion, Zeke's... take what is the best for your team ).

Some magic pen ( Lulu's spell have awesome damage early-mid game ), flat armor seals ( don't forget, there will be an AD carry on botlane ! ), flat MR glyphs ( even if she has 30MR at lvl 1 ), and some AP for some damage early game.

I use 0/6/24, which is one of the best masteries for support imo.

Glitterlance
Max this first. This 80% slow is just OP. At lvl 5, a 80% slow during 2sec = a kill for your team. Moreover it does so much damage.

Whimsy
I take it once at lvl 4 ( it's not really necessary before, even if you play aggressive ) .
Use it on an ally to chase.
Use it on this AD carry or any champ which deals tons of damage ( But focus champs like Nunu while channeling his ult, or Malzahar ... )

Help, Pix!
I take it lvl 2 and max it after Glitterlance.
Glitterlance and Help, Pix! Together will harass this greedy AD carry who wants to take a last hit ( at lvl 7, you can do around 300 damage within 2sec )
I usually use it on ennemies to harass, but in teamfights use it on your AD carry ( that shield can save him )

Wild Growth
This ult... helps you to towerdive at anytime, with Whimsy. The amount of health it gives can save a mate, even if the bump is ridiculous. It has 48sec CD with 40%CDR, so spam it :) .

Flash and Clairvoyance. Nothing is better than these, don't waste any of them for a heal or an exhaust.

You are a support, you'll want to take botlane. Any AD carry is good with Lulu, but Ashe is the best imo ( so much slows ! ) . Don't play too aggressive before lvl 4, because Help, Pix! can save you from an unexpected gank while you're trying to kill your opponents.
Use Glitterlance when the AD carry is going to take a last hit, he won't be able to dodge it easily, and use Whismy on your AD carry for him to harass.
At lvl 6 you can play very very aggressive, don't loose opportunities to snare them and pick up an easy kill. And never forget to ward !

Run everywhere, put wards, help your allies getting kills thanks to your snares and buff. Glitterlance can be a really good engage if someone is overextending. Use your ult on someone who is about to die, and shield squishies, and transform this ugly AD carry or bruiser into a squirrel !

Thank you everyone for reading this build, hope it helped a bit :) ! I'll sometimes update it, and make it more clear.

And thanks mobafire for giving me awesome build guides !