Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
If you rate it negatively please state why.
This is somewhat of a squishy build.
I will add more soon, as well as organizing it and rephrasing some bits.
During team battles try to stay back (which shouldn't necessarily be a problem considering the range of Noxian Corrosive Charge and Acid Hunter) and/or behind somebody less squishy.
The two summoner spells I have chosen are Flash and Ignite.
Flash is extremely good for escaping, and is also helpful with Urgot's ultimate. If you flash to the enemy and use your ultimate on them (and hopefully your team is behind you), it's pretty much a free kill.
Now, you may be wondering, "Why Ignite? Urgot already has a DoT spell." That is true, but if you've seen Mordekaiser use his ultimate then pop Ignite on them, you would realize that a dual DoT is extremely effective. If you have gotten the enemy low enough, which isn't too difficult with Urgot, the Noxian Corrosive Charge + Ignite combo is deadly.
I get Acid Hunter first due to the possibility of extreme harassment (which is furthered with the Noxian Corrosive Charge). The range and damage makes it possible to push them back and hopefully make them turret hug. Doran's Ring should help in the beginning by giving you some extra health as well as mana regeneration. Sorcerer's Shoes due to the fact that its magic penetration affects Noxian Corrosive Charge. The Brutalizer has armor penetration and cooldown reduction which allows you to release more Acid Hunter shots as well as do a bit more damage.
Guinsoo's Rageblade is excellent for Urgot as he is a damage hybrid. Once it is purchased, standard attacks will do quite a bit of damage. Attack speed helps out, as does the added ability power once eight stacks are achieved.
Next would be the Hextech Gunblade, which is also excellent for Urgot as it adds both attack damage and ability power. The bonus use of the Gunblade does 300 damage as well, which is quite helpful, but to be honestly I rarely use it, as it is much easier shooting them with Acid Hunter.
The Black Cleaver. Damage and armor reduction.. what a gift for Urgot. It's pretty much self-explanitory why this item was chosen.
If you're wondering why Madred's Bloodrazor is there, it is because of the sheer damage that is dealt by Urgot's standard attacks. If you are running low on mana, you can enable the Terror Capacitor, hit them once with Acid Hunter (assuming your aim is good), then bomb them down with standard attacks. The "The Black Cleaver + Madred's Bloodrazor" combo is also excellent against tanks. It's not expected to get this or the next item.
Sell off The Brutalizer, seeing as the cooldown reduction isn't necessarily needed as much as it was before. Urgot should now deal a significant amount of damage with Acid Hunter, Noxian Corrosive Charge, and his standard attacks, but adding Zhonya's would allow you to absorb much more damage with Terror Capacitor as well as dealing much more damage with Noxian Corrosive Charge.