I will like to start by saying that Shyvanna excels with a great deal of attack speed and on hit effects. I made this build to increase the amount of damage she deals with twin bite, and enhance her natural ability to apply on hit effects.

Building her with armor first, to compliment the magic resist in her runes and masteries allows you longer lane presence early game. It makes you more durable in late game.
Like i said All items but two have on hit effects.
With this build I deal a lot of magic damage, and if they build magic resist I am dealing quite a bit of physical damage as well.I changed it a bit to increase the amount of damage I put out, With buying malady, if they so build a lot of magic resist I would suggest a blood thirster instead though, maybe grab a Black Cleaver instead of Ionic Spark, to buff your physical damage.

I picked runes to help her terrible early game, so increase attack speed, some magic resist, and health. With these runes you can get some farm. It is possible to add some health regen or cool down reduction if you prefer those to attack speed.

Burnout is her main way to pick up minion kills, and is VERY usefull in dragon form in a team fight, so you want to max that first. You do want to place a point in your fireball at level 4 but max twin bite second. Of course picking up your Dragon at 6,11,16

I use teleport to be where my team needs me to be. Exhuast to lower magic resist and lets me chase down kills much mroe easily.
These can be used instead, flash, ghost, and even surge for the attack speed boost

I focused her masteries, like her runes, on buffing her early game play. With the masteries that I use out you have raise attack speed, and the ability to destroy towers.
The tank masteries that i use it gives me better staying power with magic resist and health.I have made the early game tank along with the extra gold with kills to get o her late game faster, and this has helped me tremendously.

during team fight you really do have to time turning into a dragon. You should wait until you can cause the most damage, be it by chasing the enemy team down, or by knocking the enemy team around. using burn out and twin bite allows you to really destroy a whole team as once.

In summery, Shyvanna is a wonderful endgame champion that relays on attack speed. I will play her more, and take into account the comments on this page, and I will update, happy playing.