Hey. There's this hot girl in my highschool which has recently moved in the next building.
I tried hiting on her last year, but can't remember what happened .
She's hot but not the popular bitch type. I want to befriend her; we're neighbours, we should talk! ) Also, she's a good DHV source as she has lots of girl friends.
We don't see each other much.

How and what should I say to her? Facebook is kinda the only possible way of interaction.

Facebook is impersonal when you have common ground such as study and lives local. I'd suggest going to similar places she goes as this should be target rich anyway and go up to her and your opener will be her name i.e. jess

Urm...why? adding her on facebook will seem weak and AFCish. Adding a girl on facebook should be last resort because its physically impossible for you to get in contact with her.

She lives next door to you. The best possible way of interaction is to walk over there, knock on her door and bossman it. I can guarantee that most guys that interact with her take the easy text/facebook approach.

You: Oh Hi there, I noticed you moved into the area. Thought I'd say hello.

Her: Oh hiiiii. blahblahblah

Get rapport make her laugh then hit her with

You: Hey I'm just off for a drink, you should join.

If she makes up/has an excuse then go for number close aka "Ah next time I'm free then, whats your number?"

if she's up for it, standard process. Take her out, have fun, escalate, go for k-close/f-close.

This not only increases your attraction no matter what as you don't bullshit around what you want but you can also gauge how cool she is about this kind of thing. Facebook will just show how dependent you are on non face2face communication. Plus if you add her and she accepts, she asks "Where do you live" and you say "right next to you" then she will just lower your value by saying something like "Why didn't you come say Hi?"

Easier said than done. She lives with her parents and it would be kinda awkward, but it must be done ).

We're already friends on FB (since 2012); she moved "next door" this summer.
Also, I have classes in the morning while she has them in the afternoon and no matter what, I can't seem to bump into her at noon (nowhere!).

Seriously...stop being a pussy mate. This is even more of a reason to do. Bossman an interaction to her parents infront of her = you're the fucking man.

Think about it...what other guy has done this??

Plus if her mum digs you...you're in.

Even if you fail/it goes wrong you can stand proud and say to yourself "I fucking did that" which will improve your inner game anything over facebook you'll overthink = damages your inner game.