Yo! Welcome to my first build.
This guide is about LeBlanc and about her burst potential.

Pros:
[*] Insane burst
[*] Domination at lvl 6
[*] Hot!
Cons:
[*] Terrible farming skills
[*] Easy target from CC
[*] Terrible early-early game

For runes I'd like to build maximum ability power as much as possible. This means that you can one-shot the enemy carry right away.

Typical AP masteries not much to say.

As you know, this isnt the only way to build LB, however the way i build her is to maximize her AP along with her CDR. Why CDR? because not only will your ult refresh faster(1 burst per 14-15 sec) but also your abily to chase or run will increase in probablity.
I don't really like snowball items as they aren't as always cost efficient.

I take Snare at lvl 1 the reason is to gank at lvl 1 if needed, it also will deal more damage than the sigil, and a snare is also benefical for utility.
I max Sigil ASAP as sigil id my main dmg dealer.
Once you get to lvl 3-5 you can harrass the enemy by using W->Q->E combo. This allows for more of a burst than dmg.
At lvl 6 if you have the suffienct mp, let your foe push(if he isn't doing so already) use W->Q->R->E and ignite during the snare for maximum dmg. If he didn't die already, chase until sigil becomes availble again, this is why you should wait for a counter-push.