This is just the basic build I use when I play Varus...which is quite often. Played correctly this build can carry you whole team.

P.S. Works for both Summoner's Rift and Twisted Treeline, it wouldn't let me select both.

These runes focus on dealing damage fast so you can get out of danger. Since it's a, AD build, the armour penetration is key and the attack speed helps boost that DPS output in an incredible way.

All these items focus on attack speed and attack damage, some can be substituted for something like armour (if you don't think you can get away fast enough).