*disclaimer: This build is good, but that doesn't mean that it is set in stone; thinking out which item is more immediately necessary at certain points in the game is crucial to playing any build.
This one's more geared towards getting attack damage quickly. Special notes would have to be get manamune asap; its effect is better based on how quickly you can aquire it. To that end I might suggest getting it before which boots you require at the time. You'll notice I listed Mercury's Treads on the build; however which boots you choose are entirely situational. If you need to shorten stuns Merc's treads are great, however ninja tabi are better for fighting melee-oriented teams, etcetera. Other than that, I'd suggest getting Phage first while working towards trinity force, because zeal is attack damage, and sheen is AP, however in certain situations, where you want to hit more quickly to do more damage, choosing zeal first is viable. Also Sheen is good if you find yourself constantly out of mana. After this point you can continue to stack AD; or if you keep on dying in team fights go for Guardian angel before investing in last whisper/ Black Cleaver. That's all.

Urgot is a ranged dps.
You should heckle early game with your acid hunter, and get you noxian corrosive charge next. Snag an shots you can with just acid hunter, but use your noxian charge to allow you to home in on your target if they continuously run away or into bushes. To home in on your enemies, shoot your charge and, while your enemy is coated, hover your cursor over their champion. Your Acid hunter should fire up into the air and hone in on the enemy, who should have a red reticle underneath them, if you've aimed correctly. This can be crucial if, say, you've coated a lot of your creeps with your charge, or you want to single out a champion when you've coated both enemies.
Urgot's shield can slow people, so use it as an escape or a tool to slow fleeing enemies, alternatively. This build puts less emphasis on this skill till late game.
Your Ultimate skill can switches your location with your enemy, as well as granting you increased shield for a time. Use it to hold fleeing enemies, pull enemies, or, in a pinch, to help yourself flee (this is difficult). Using this skill to pull enemies into the range of your turret is an excellent way to get some kills. While your ult will shield you, you'll be very vulnerable when you switch places with an enemy if his team is nearby. Be sure to have your shield ready and to slow pursuers while you flee.