Here's how it goes.

1. Boots + 3 Pots
2. Boots then go into berserker's
3. Build the razor part of wriggles first then complete it for warding and sustain
4. build the phage then into a frozen mallet
5. build the brutalizer then into the ghostblade
6. build a hexdrinker into the maw
7. Build a GA (chain first or the cloak once again depending on the situation)
8. sell your wriggles for a bloodthirster (bloodthirster needs to be brought out-right do not sell the wriggles untill you can afford it e.g. say wriggles sells for 1.2K sell it when you have 1.8K)

You wanna max your Q first but get all your moves asap.

Q at 1, W at 2, E at 3

Maxing your Q first gives you some good minion farming as well as combos in a stunned enemy champion.
Maxing your W second gives you a nice stun with some decent damage to go into your Q, Q, Q combo.
Maxing your R third (like most people) gives you an excellent buff as well as the ranged finisher if you feel that ignite won't be enough.
Maxing your E last is good for initiation as you combo their team with yours at your back with the combo of R, E, Q, W, Q, Q and by this time a kill (other than the already dead champs from the teamfight) should be able to be finished off by your R's ranged attack.

All and all the mastery page is your own choice this is what i use for her though.

The rune page is there for some extra AD and stabilization in the lane and well as some starting armour pen. never hurt anyone (but your enemies)