Precision Tree:

Press The Attack:
A great Rune overall, offers great damage.

Triumph:
A good all-around rune, great for 2v2s and other fights in the early game.

Legend: Alacrity:
Urgot scales pretty well with attack speed. After level 13 his passive gets a 2.5 second Cooldown and paired with some attack speed he becomes a monster.

Coup De Grace:
A great Rune for taking down enemies with low health. Combos well with Urgot's ultimate.

Inspiration Tree:

Perfect Timing:
The free Stopwatch is really good for almost every champion in the game. Take this Rune if you're going to build Guardian Angel later in the game. If not take Future's Market instead.

Cosmic Insight:
Great all-around Rune, great for Urgot since his Ultimate can be used to kill enemies. Lower Cooldown on Ultimate = More Kills.

Core:

Black Cleaver:
A must buy for every game. It offers great stats like Hp, Ad, Ms and Armor Penetration. Your W applies Black Cleaver stacks which makes for a great Combo. Nothing much to say about this item, take it.

Frozen Mallet:
As mentioned before, Urgot's W applies on hit effects which includes Frozen Mallet. In terms of raw stats it offers great tankiness, which is essential for Urgot as he's needs to be close distance to kill his targets.

Boots:
One type of boot is always a must.

Aggresive Items:

Death's Dance:
This is a great item for the mid game if you're ahead or even. It offers good damage and some life steal as well as CDR. If you're behind you might want to buy something more defensive.

Guardian's Angel:
Almost a must-buy for every game, it's just that this item is better to get a bit later into the game. If you went for the "Perfect Timing" Rune as i recommended this item becomes 600g cheaper. This item lets you play a bit more aggresive in skirmishes as well as teamfights. Great item for Urgot as he often stands in the front of everyone, which means he can easily get the item used.

Lord Dominik's Regards:
Great item if vs lots of heavy Hp champions. This paired with Black Cleaver can shred tanks.

Mortal Reminder:
Very situational. Good vs champions with a lot of healing, for example Swain, Soraka or Vladimir.

Defensive Items:

Randuin's Omen:
Great item vs heavy Ad comp. Offers great stats as well as a sweet active. The active is easy for Urgot to use since he often finds himself in the middle of the enemy team.

Frozen Heart:
Great item vs heavy Ad comp. This item gives you a lot of armor which is nice. Good vs team with a lot of champions that rely on attack speed. This item is especially nice if you want that extra bit of CDR. I highly recommend this item for Urgot. Note: Don't purchase Frozen Heart and Randuin's Omen in the same game as the passive doesn't stack.

Thornmail:
Good item paired with either a Randuin's or Frozen Heart if vs all Ad.

Maw of Malmortius:
Great item if vs ap laner or team. Offers Ad, Lethality and Mr.

Boot Options:
Swiftness boots if ahead, offers slow resist and a nice amount of Ms. Ninja Tabi can be a great alternative if vs Ad laner or heavy Ad team. Mercury Treads can be a great option if vs Ap but mostly hard CC. I included Boots of Lucidity for those who didn't get the max 40% CDR into thier build but feel like they need to, it's not a bad option for Urgot.