That is a terrible build. Don't feel bad... I did the same thing, as have most people.
Xin is a melee champion that is a pure autoattacker. He actually has solid burst damage but like all autoattackers he does damage over time.
Except instead of being behind a team shooting at 700 range like Kog or Trist, he is right in the middle of them.
This means that you are squishy and very threatening. You will get killed in about 1 second. Dead melee does no DPS.
Therefore you need TANKINESS for mid to lategame. After the armor/MR nerfs especially and due to the fact that Xin can get up to 125 free armor/MR, your main way to tank up is HEALTH. Lots of it.
Tankiness early on also lets you trade better toplane and have a better chance of surviving jungle gank.
So I would recommend starting with a ward for sure to avoid ganks ,rejuv bead, pots. Or cloth+5 if you arent as worried about inital gank.
A brutalizer is a good typical first item on Xin. He already has decent regen and brut greatly increases damage due to armor pen and AD.
From there you want a Giants belt and get a Warmogs. This hugely increases your tankiness and sustain. It also makes you able to fight midgame and you are a great initiator.
Now you can get the Black Cleaver or a Ghostblade, then get a brutalizer and the one you didnt get.
I prefer the Ghostblade because it synergizes so well with Xin. He charges, Ults for armor/MR, Facerolls for 80% AS, increased spear dmg, knockup. It all lasts for about 6 seconds. Ghostblade adds big chasing ability thru MS boost and another 40% AS to get in as many hits as possible.
Cleaver adds even more health and the 25% armor penetration over time effect. Both the armor pens stack which is very nice.
You likely get Merc Treads since autoattackers that are slowed and trying to catch an enemy deal 0 DPS. (unlike bruiser that has a slow AS and AD-based abilities with CDs anyways).
Got room for 2 more items.
*Aegis adds extra tankiness if your support and jungler arent getting it.
*Infinities Edge adds a **** TON of damage if you are surviving ok.
*Brutalizer adds even more AD, apen, CDR. Will be dead weight though since u cant upgrade without losing its apen/CDR.
* Hydra is an option. Its not very cost-effective though. Lategame I'd rather have crit.
* Atmas. strong. Big endgame AD, crit, and extra armor for more lategame tankiness.
* Last whisper - yet more armor pen. 35% here, 15% passive, 8% mastery, 25% BC is over 1/2 armor stripped, then youve got a ton of flat APen from your rune/mastery+2or3 items.
* Another warmogs adds even more survivability. Remember, with +125 potential armor/MR for free, health adds themost effective hit points.