Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
This build is taken from the Riot YouTube video build. I wanted to have an easier way to reference it. I did this for myself and anyone else who may want a quicker reference to Riot YouTube build.
(The following descriptions are also right off of the video)
The main goal of this build is to farm, kill towers and support team during team fights.
From level 3 and on you can gain a lot of free gold from going to the wrath camp and smiting the blue wrath and then killing the other three with boomerang and ricochet and obviously pushing your lane.
At level 8 you want to get the blue buff which is important to this build. First kill the little guys with boomerang and ricochet. You then want to pull the Golem into the brush so you won't be seen and time your smite so its close to your last hit.
If your ever near the enemy's blue buff don't hesitate to gank it with the same tactics above.
At the 15 min mark you can easily take down baron with your team and buffing them with "On the Hunt" & Rally (if its up) and quickly dispatch baron before the enemy team knows whats happening.
Always join team fights to help support your allies. With all your team buffs you can quickly help sway the fight. As well as push towers every chance you get. With Sivir's incredible pushing power she can slice through lanes like butter.