When I 1st started playing Urgot I was using Crabpeoples' Pride. Now You can no longer find said build as it is discontinued (this may change I'm not sure). This build resembles Crabpeoples' in many ways, this I know, I'm not trying to rip off his build. I'm only saying by making the basic items/runes the same: Why fix what isn't broken? This good part about Urgot is that whats done is done, he is probably not going to be nerfed any time soon and the items that you get for him (if you follow this build) aren't a big deal, they're simple and easy to see how they work for him.
Urgot is a good Champion because of a few key points: 1; he is often under/over-estimated this causes allot of people who haven't seen him to back off or walk into a situation that is ideal for him to kill them (like tower diving), 2; he is a very utility oriented champion due to his ult/slow/auto-target meaning that you can be doing bad in the game one minute ult a team member of theirs into yours and be responsible for a successful team fight (very few champions can be truly effective in team fights if they haven't been doing well), 3; he is one of the greatest pokes in the game with his E and Q combo
My experience with Urgot is from standard non-ranked games (I've only played one ranked game with him, and got 9/0) feel free to criticize this build for not being truly tested in ranked, but it works and I leave it for you to test and find out.

Crabepeoples' build goes off of these and gives a few alternatives, but the main reason for having these in particular is
A: Urgot is very mana hungry at the start of the game and the seals help with that
B: Flat CD may cost twice as much ip, but the most logical way to build your rune page is for early game only (Many items outclass what a full rune page can do. So runes are only good for the point in the game were you cant afford them)
C: Armor penetration rapes the early armor of some champs, as in the items they get. and since Urgot only does physical dmg it kinda sucks when you have to lane against a Irelia with a Doran's shield and your Q hardly registers on her health bar

I saw the armor penetration mastery in the new Offensive mastery tree and I knew i had to have it, the cool down reduction is excellent and brings your total cd at the beginning of the game to just under 10% (Little less than a brutalizer, and with it almost a Frozen Heart)
Armor and magic resistance make early game attack trading better for you against most other champions, and more health regeneration never hurt anyone.
keeping buffs on you longer is a good deal for when you find you've killed someone with a blue buff and you want to make them regret meeting you on the opposite team, extra mana regeneration helps in lane sustain. (the cool down reduction of flash and ghost is self explanitory I hope)

I'm not ripping off the Crabpeoples' build so much that I couldnt give you alternatives to some items.
Meki pendant and health potions for early game lane sustain. Try not to go back again until you've killed your lane opponent (Think with your head muscles and realize that doesn't mean I want you to get killed rushing in to get them before you go back, if your having a hard time go back and get stuff)
If you've been farming inteligently (ei farming with auto attacks and Q last hitting when needed) you should have enough to at least upgrade to tear and get regular boots. You get a cookie if you can also get the long sword for your Manamune.
After Manamune you should grab Mercury's Treads and start on getting the Brutalizer (WARNING: do not sell Manamune EVER, this is a key item to Urgot and should never be sold! Sell Brutalizer instead). This is were things get fun!
You should always think of the team ahead of yourself and get Aegis of the Legion after Brutalizer, but after that it depends on things like enemy team composition and how much you're carrying your team. If you do allot of the killing on the team it might be better to start building like a carry Urgot, here are some of the items i recommend for that:
1: turn Brualizer into a Youmuu's Ghostblade for the extra armor penetration, coll down reduction and attack dmg
2: Rush Last Whisper after upgrading your Brutalizer for the armor pen as the enemy team will probably start building to counter you
3: Consider turning your Aegis of the Legion into a Guardian Angel for the resurrection and the added armor and magic resistance to you
4: While I've never built this on Urgot myself it would probably be a good idea to switch your Mercury's Treads for Ionian boots of Lucidity for the added cool down as Frozen Heart will most likely not be a priority anymore (With Ghost and Flash Summoner Spells you can easily escape from most situations anyway)
5: Everyone has a different opinion of what other dmg items work for Urgot better be it Bloodthirster or Infinity Edge, I don't really care which you go for they're both good choices (I go for Infinity Edge personally because it is more stable in dmg and the lifesteal from Bloodthirster doesn't take life from your Q anyway, neither does the critical strikes Infinity edge but still.)
Under normal circumstances just follow the listed items at the top of the build as it will give you the most utility to your team while still doing decent dmg (again think with your head muscles and build according to the enemy team comp as well, if they only have 1 ability power champion it might be better to get Frozen Heart 1st after Aegis or the Legion. If they have allot of burst on their team go with Banshee instead of Force of Nature. ect, ect)

Q is a good farming tool. Only need one point on E because you only get it for the auto lock anyway. Flip Flop W and Q because the slow and shield gets stronger and Q does more base dmg the higher level it is. Upgrade R every time you can because that's what all the kids are doing these days.

Try to solo lane whenever possible, if not, take a stun/snare champ with you so you can land your Q and E easier. If your laning opponent is tower hugging you're doing your job right, when they are tower hugging try to make them over extend a bit to land more E>Q combos. Try to calculate the dmg they take from each Q when you lock on, you can use this to know when to tower dive and kill them (Urgot is actually a really good tower diver because he can out-range the tower and his shield can tank one or two hits from it before being taken offline). Never rely on your E to kill an enemy, it happens but it isn't practical to let a kill go because of it. Urgot's main challenge in lane is a teleporting champion (katarina, Ezreal, ect) as, if they are smart, they will make you waist your mana and E shooting for them and then teleporting out of the way, after your E is wasted you lose allot of your dmg potential if they rush you.

I would love to hear your feedback from trying my build (if you would call it mine). In a sense this build is a tribute to Crabpeople's Pride as it was my 1st build I Tried with Urgot and it lead me to take up Urgot as my main and find out how amazing and unique of a champion he is. So this of for you Crabgot- the Crabpeople's Pride (except I prefer rocket powered Chainsaws to a crab claw).