Yes, well, this is my first guide so I will be updating this a lot.I'm just going to upload this so I can remember my Xin build but you can use it ^^.

I take Greater Mark of Desolation because Xin is best built on armor pen with speed.With that said, I take Greater Seal of Alacrity for that extra speed.
Now, Glyphs are your choises but It's recomended to take either magic resist, mana regen. or cooldown reduction glyphs.
I, myself, take magic resist to stay alive longer against heavy spellcasters like LeBlanc, Brand or Veigar.

Haven't quite figured out what to do with the extra 2-3 points but 24/6/0 suits me well enough, giving me the extra armor and magic resist.

Most complicated builds.
Start of with Dorans Shield, the next item depends on when you will be getting back.If you don't have enough money for merc. treads then buy Boots and a dagger.From there, complete your mercury treads and start building The Brutalizer and finish your Youmuu's Ghost Blade when you have the money.(Keep in mind that getting an early Zeal helps you aswell, but if you play like a pro then you can handle that slow attack speed until you get Youmuu's.)After that get Zeal or Phage, if you didn't build them before.If you get Zeal, then finish with Phantom Dancer and start building Frozen Mallet.(Another thing is heavy armor based champions like Malphite, if you're against someone like him, it's recomended to take Last Whisper after Youmuu's and skip Frozen Mallet before Phantom Dancer.)The next 2 items will be totaly your choise.Best to get life steal with that tremendous attack speed so Starks Fervor is a good item if your team doesn't have it.

Haven't gotten to the 6th item yet. So this will be left unfinished for now.

Alternative route is to get Q, W, E level 2 and then start leveling Battle Cry if you skip the dagger.

Ignite and Flash is what I use, but getting Exhaust instead of ignite is awesome aswell.
You won't really need Ghost because you will be too freaking fast at the end of your build.

Best way to utilize this build is to attack RIGHT AFTER a tank has initiated.Charge your way in and ultimate to destroy most of their health.
If you have good teammates, able to stun or silence the dps, then your mission is to get rid of the carries and off-tanks.

You can use Battle Cry to push and farm quickly. It costs a few mana that you're able to regenerate fast.

With Mana Regen Glyphs you are able to use all of your skills to farm.

You're fairly squishy at start and easy to take out if there is someone like Master Yi or Nocturne on the opposite team, so stay wary of ganks and don't rush in all the time.

Hope you liked this guide and I hope you'll use this :)