I've found a nice build for Sylva but i have not the time to write a guide, sorry. Make it what you want !

Barbed Shot : Control and kill mobs faster.

Envenom : Finish ennemi players.

Follow Through : Renforcing the basics damages with Barbed Shot + Basic Attack

Wailling Arrow : Zone damages and control the ennemi players on teamfights.

Splinter Shot : Increase your push capacity.

Cold Embrace : After put this, make your opponents more weak and kill them.

Fury of the Storm : Destruct all AI ennemis very faster. And gain a powerfull damages on a single target. Every 5 seconds.