Urgot is all about armor penetration, and since you don't only reduce the armor for yourself you actually do very much for your team, especially for assassins with Last Whisper. Imagine a Rengar or Talon with a lot of flat armor penetration combined with the percentage armor pen from Urgot. I also think that support Rengar works very well with Urgot since support Rengar builds cheap flat armor pen items.

About the Build:
I believe that regen is the best Urgot start for any lane. He scales well with AD but he runs out of mana very fast. The core build for Urgot is obviously tear since Muramana is a crazy item on him and he stacks pretty quickly. Also he scales well with AD which is why many people build Frozen Heart for the extra 8 AD through Manamune's passive. Urgot works extremely well with cooldown reduction because he will be able to spam Acid Hunter more often. You want to max his cooldown reduction with CDR items. Black Cleaver is absolutely core since it not only gives percentage armor shred that works well with his Noxian Corrosive Charge, it also gives flat armor pen that works well with percentage armor pen and it gives a lot of flat AD, health and finally closes the CDR gap in a full build. For the big CDR item I go for Spirit Visage over Frozen Heart, I feel like you get a lot tankier with the combination of health and resistance than just resistance, SV also costs less than FH. You can purchase armor early for laning and get a Warden's Mail in the mid game while you continue your item path. Last Whisper can be purchased earlier in the game but is definitly core on Urgot. This build focuses on getting really damn tanky while helping your team with armor shred, that's why I choose a big tank item as my 6th item instead of Bloodthirster/Triforce/MoM.
For Boots I choose Tenacity for obvious reasons.