I main Jungle Xin in ranked with over 75% of my ranked games as him (though that may soon change).
Phage early on is very useful - health, a supplement slow and some AD. Getting the crystal lets you dive. The AD scales with your abilities and autoattacks. The slow is great in ganks and for chasing. It builds into either a Trinity Force or a Frozen Mallet. One is defensive. The other is offensive.
Tenacity is almost a must - you will get CC'd a lot...
Machette can be upgraded to Spirit of Ancient Golem for Tenacity, HP and Armour in place of Mercs. Allows you to Jungle/Dragon/Baron quicker, or use alternate boots like Tabi (against heavy AD/auto) teams or Mobility Boots (troll/stomper build)
Blood Thirster > Infinity Edge because of the cost factor and you're not a Crit champ
Hexdrinker is useful early on against strong AP Comps, turns into a Maw of Malmortius later on
Ravenous Hydra is a horrible item to get on him - you're more that capable of pushing and downing towers as it is and you don't really benefit from the AOE
Sample Xin Builds:
(Assasin Carry - Fed Xin who deals tonnes of damage, takes out priority champs very quickly)
Mercs Treads, Trinity Force, Bloodthirster, Bloodthirster
Spirit of the Ancient Golem, Ninja Tabi, Blood Thirster, Frozen Mallet, Randuins Omen, Black Cleaver
Mercs, Frozen Mallet, Maw of Malmortius, Blood Thirster, Mercurial Scimitar
(Super Anti AP - only happened once in ranked against a team that was very strong)
Mercs, Frozen Mallet, Maw of Malmortius, Mercurial Scimitar, Banshees Veil, Blade of the Ruined King (I didn't have the hold for a BT.)
(General Tanky Bruiser)
Mercs, Frozen Mallet, Bloodthirster, Black Cleaver, Black Cleaver
(AD Debuff King - Troll build that uses your Ult to debuff as many enemies as possible while having epic Armour shred and Arpen)
Mercs, Black Cleaver, Black Cleaver, Black Cleaver, Black Cleaver, Youmu's Ghostblade