As a samurai, this Master Yi has to prove he has the skill to slain all his foes with his masterwork B.F. katana, and enough guts to parry their attacks with his armor.
Unlike the typical Yi, his fighting style is not the one of an assasin striking from behind when the teamfight has already begun, he'll just banzai charge his foes to crush them all.

Well, this introduction is more realistic than it seems at first sight.

This is a build that allows to survive teamfights as a fighter as well as turret diving when going for a gank. It needs to jungle and gank a lot to farm that lot of money needed to buy this item combination.

I usually start killing ghosts, smiting the bigger one, then go for the wolves. This order avoids getting killed when killing the golem, which has to be killed at level 4. Don't mind going back when you have low hp, you would have to go back whether you take the blue buff first or not.

After killing that wolves, go take twin golems, then recall.

Time to take the blue buff for the first time, you'll have level 4 at least when you have it, maybe you want to take the red buff, meditate a couple of times and start gankind at will. Take care, you probably won't have boots nor Highlander, so you will have to rely on your red buff and your exhaust.

Take a gank, maybe two, recall, buy boots and some lifesteal, and you are free to take the whole jungle on your own. You should be able to kill the dragon by yourself at level 10-11. If you need help, gank bottom and ask for it.

Gank. Gank. More gank. Critical runes will help you, if you are lucky enough you will take the kill faster. By the time you have your third gank, you will be starting to carry your team, able to kill most of the enemies 1 on 1.
When the late game comes, as an offtank, you have to focus well, but you have no cc nor support, only attack and survival, ensure another carry takes some kills when you gank so, when teamfighting, you have another damage dealer on your back to kill your enemies when you have too many aggro and you are meditating.
Enter the jungle as much as you can, share the four available buffs (you are THE jungler, you own your team's and the other's jungles) with your team mates, and help when they are taking them, you will need them to pentakill and to be the last man standing, but it's better if your whole team survives.

Use your q.
Attack when you have enough lifesteal to kill a bunch of minions and end with full hp.
Just RUN when you are farming and smell a gank. If you can see at least 4 characters far from you, warn your team you are going the backdoor way. Take the next turret. Don't be afraid of diving to kill the 5th enemy, the one defending the turret, unless it is an offtank or a tank, in that case... just think it twice. that will probably hurt.

Early game-> Crit, aspd, lifesteal, ad in that order. Mid game-> After you have your shadowdancer and your bloodthirster, build warmog. Late game-> End your ad and critical with Atma's Impaler and Infinity Blade.

Variant-> Maybe you can use better Berserker's Greaves first, and then change to Mercury's Treads, when the whole enemy team is focusing you.