First of all, I am not claiming to be the best urgot but i seem to have pretty successful games with him and I thought I'd share my builds. The First build is trial dmg build on him, although i normally play the second one simply because of the survivability. But just like alot of the other awesome helpful urgot guids explain, you need your core items first.

Core Items
Manamune

Boots (any kind you like, i tend to get CD reduction or swiftness)

Brutalizer

after these items go ahead and grab the items listed in the build. You have to remember when playing urgot that SKILLS DONT CRIT with him. So Infinityz Edge's passive isn't as great as youd probably like. If its your first time playing urgot id build the tankier one. You'll have more fun and not be so vulnerable endgame.

Summoner spells
I recommend always a flash or a ghost, he tends to be a little sluggish early game if you dont get boots of swiftness, although that could just be his waddling crab walk fooling me.

Team Fights
Ulty out the tank, lay down a spray of your corrosive and pick off the most dangerous/fed one.

Laning
Harass, Harass, Harass. With his acid hunters range you can pick off hilarious, almost turret diving, ballsy kills that make you LoL. Dont get too greedy tho. If they have you pushed to your turret you can always use your ulty to bring em into the turret when their on the edge of their creeps and ruin their perm with its lazer.

Ganking
Ehh, i tend to leave it to the jungler, but if your playing mid, just like any other gank, wait for them to cross enemy lines and pounce, and remember to put your shield up for the slowing effect it had. AND USE YOUR ULTY IF THEIR GETTING AWAY!!!