Yasuo, the brand new hero on the LoL pantheon, is a very unique concept. It builds up with Critical Damage and attack speed, as some of the best AD Assassin heroes would. This build is based on Attack Damage and Critical Strike, using the benefits of the Passive Hability and the Ultimate's armor penetration buff.

When you play Yasuo top lane, solo or dual (which I don't recomend) you should keep in mind that your opponents will be tough. Not necessarily hard, but tough. Garen, Darius, Tryndamere and Nasus can build up both in armor and HP, so you must have sustain in lane. The Blade of Doran and a single potion should do the trick, if you stay away of harassment.
Concerning movement, notice that you have two good options. The Berserker's Greaves will add up in your attack speed, decresing the cooldown of your Q. The Boots of Mobility will increase the rate of regeneration of your passive's shield when out of combat. If you will play more safe, the BoM is a good option. If you play more agressively, the Berserker is your choice.

In the first stage, you'll start to build up both crit and dmg. The Zeal will do the trick on the crit and atk spd, and the Vampiric Scepter will give more sustain, specialy because your crit rate is doubled: With all the itens of this stage, you will have a 50% rate of crits already. Add another Longsword, to escalade to your stage 2.

Here is where the magic realy starts. At this point, with the Ghost Dancer, your crit chance is at 60%. Plus, your Q's cooldown should be ridiculously fast, and your shield is constantly charged. Add some more life steal with the Bilgewather Cutlass (wich give some 100 more damage and slows the target), and go for the B.F. Sword.

When you're at this point, you can choose one of two paths. The first will ensure your enemies will never flee. The E, combined with Flash, the Frozem Malet's passive, the Blade of the Ruined King and the Mercurial Scimitar active habilities, will make it impossible for the victim to run away. This stage 3 build leads to the ultimate Yasuo's Assassin role.
If you choose the other build, You will have tons of damage as well, but will control lanes and TF's much better. It focuses on armor reduction (wich builds up with the 15s ultimate's passive armor pen buff) and area damage. Since the Q is affected by any on-hit efect (crits, life steal, passive items habilities, etc.), you'll devastate any TF with it.

With the 1st "Stage 3" build, you'll have (items only): 100% Crit Chance, 240% Crit Damage, 185 damage, 15% Life Steal, +700HP, +45 Magic Resist, more mov speed and 40% slow on hit.
With the 2nd "Stage 3' build, you'll have (items only): 100% crit Chance, 240% Crit Damage, 210 damage, 27% Life Steal, 15 Health Regen/5 sec and ignores 35% of armor.

That's it. This build is focused on AD and the role of Top Assassin, which is the best for me. Rate it, so I'll know I'm good or not at this "strategist ****"... hehehe