Starting Items

As Yasuo you want to be able to clear your jungle. Hunter's Machete is the best go to item to do this. On top of that the ability to carry 5 health pots for sustain is very helpful. It is pretty self explanatory, most junglers will start machete and clear. This item also sets you up to get your spirit stone early. The red trinket is great for sweeping wards off the map. Communicate with your team mates to help you decide where you activate your sweeping trinket to clear a ward. The 5 health pots should be periodically consumed while jungling to ensure you are healthy enough for at least one gank after you clear the jungle and have both your buffs.

Core ItemsYour core Items should be Spirit of the elder lizard, and Statikk Shiv. Elder lizard not only brings damage but the passive effect helps you sustain within the jungle even on low to no life steal builds. On top of that it amplifies you clearing speed and rewards you for ganking with passive gold that builds up when not jungling. It provides a good source of a decent amount of damage as well as cdr to help you get your steel tempest knock up off. It is a very reliable jungle item on Yasuo and the sustain it offers is incredible.

Statikk Shiv should be your secondary core Item as it offers great synergy with your passive shield and dashing. By being mobile in fights and chasing as well as moving to help your proc your shield you are benefiting twice over. On top of that the critical strike is doubled. The attack speed it grants actually also lowers the cooldown on steel tempest making it much more spammable thus procing the knock up much more often.

By combining these two items you are able to clear your jungle reliably and gank/duel accordingly. The movement speed granted by statikk shiv helps you chase and gank enemies as well. You can opt to upgrade boots after or move onto heavier and stronger endgame items.

Endgame ItemsThe end game build on Yasuo should do a few things. A solid end game Yasuo build should make full use of his doubled critical strike to reach the 100% cap. It should supply significant damage as well as life steal. As Yasuo you also want to be benefited for using any of your abilities. With those guide lines in mind I will explain what each item does for you.

Spirit of the Elder Lizard - This item is your jungle clear and sustain as well as early damage. It grants CDR. This item is later sold for an alternative or stronger item. See the next section for details
Statikk Shiv - SS works with your Passive and kit to deal awesome damage. It rewards you for being mobile and moving around to help proc your shield. It also offers good wave clear on top of your already good kit for wave clearing. By being a large source of critical strike it helps boost your mid game
Infinity Edge - IE utilizes the full potential of critical striking. It is a huge damage spike for Yasuo. On top of that it gives a huge 50% critical strike chance on Yasuo. This item should be a mandatory item on him into the late game. It benefits him greatly
Blood Thirster - BT is great on Yasuo as he needs a good source of lifesteal. On top of that he has pretty incredible damage scaling on both his steel tempest and his Ultimate.
Trinity force - Benefits him for using his abilities on top of that it also boost him to reach his max critical strike. The mobility it adds also helps stack his shield much quicker. It is a great final item but it can feel really underwhelming when you build it early.


Alternative Items

With the note that all Tanky items appear to be relatively useful on Yasuo I will discuss my choice of 6 Items to replace the spirit of the elder lizard.

Ghost Blade - This is a good early snowball item. Late game it can fall off and feel underwhelming as he doesn't benefit from sheer chasing as much as others do.
Maw of Malmortious - This is a great magic resist defense item that also grants a shield that can save your life. It can lead to some pretty epic baits when fighting magic damage dealers on top of your focus shield
Blade of the ruined king - Good item vs health stackers, It can help you chase and stick to enemies as well.
Hydra - Amazing for bursting teams. If you are in a good AoE composition and can get deep within the enemies with your steel tempest knock up and ultimate you can demolish teams
Black Cleaver- Probably my preferred replacement as it grants CDR and penetration into the late game. It is universal penetration for your team making you a even more effective addition to your team
Mercurial Scimitar - Great vs CC and suppressions. Not much else to say about it, grants good damage