As someone who has been playing a great deal of Urgot as of late I can agree his need for some attention. Not necessarily a full on rework, but he does fall off noticeably hard by comparison to many other champions.
I don't particularly consider his kit to be lackluster, but there are certain quality-of-life changes that could certainly make him more relevant while not drastically affecting his playstyle.
Firstly, Urgot in his original inception (as well as his current role listing) was designed as a marksmen. Particularly in this meta which is focused on high output via Crits Urgot struggles to contend. He has a fantastic dueling kit, but said kit is reliant on builds which supports survivability and CDR as opposed to flat damage. I think his passive is incredibly relevant and wouldn't change it, but at an auto attack range of 425 he has the lowest of ANY ranged champion (http://leagueoflegends.wikia.com/wiki/Range). Even if the design of Urgot were to shift him permanently to top lane (where he's strongest in this meta) there are a plethora of champions who have either hard cc or a gap closer that can easily reach him. I would like to see his range get a slight buff to 475/500. This would give him sufficient range to contend with enemy Ranged champions which doesn't rely on his Q/E harass while not so much that Melee champions can't engage. A higher auto range would also help to alleviate early laning issues where has to spam Q to get farm while under pressure from an overly aggressive enemy Summoner.
His W and E are in a good place, presently. W is a strong shield which doubles as a slow on his Q, and E gives armor shred and at least 3 guaranteed Q hits. Both of these are quite powerful, particularly in a meta filled with tanky dps. Not only this, they can assist in securing kills which otherwise might be lost by others due to a 1200 range granted by his E to the Q.
Urgot's ult is a powerful tool in its utility. Not only assisting in repositioning, it can be a valuable tool for team fights or 1v1 engaging due to the stats granted by it. That having been said, the Range on it is quite lackluster. At 550/700/850 respectfully, it can be quite difficult to use his ult on your conditions. At such a short range many champions can simply flee either by micro or skill shots. Very rarely can his ult be used as anything other than a way to initiate a fight. If I'm attempting to chase someone down so I can reposition them to continue aggro very rarely do I find myself in a position where I can do so reliable without burning Summoners or using a combination of E/W/Q. I would like to see the Range on this boosted to a flat amount of 750-825 at all ranks.
A third and most notable off all the aforementioned weaknesses is his movement speed. In his present incarnation I think Urgot is best defined as a tanky dps, knowing this it can be very difficult to handle Urgot effectively with such a low base movement speed. At 335 base he caps at 380 w/tier 2 boots. I've never found reason to include movement speed into his build (beyond the passing fancy with Tier 3 Alacrity) and as such this can make it very difficult to position Urgot adequately, particularly as tank is such a core to his build and being able to intercept enemy Champions is important. I would like to see Urgot given a base of 345.
As you can see based on my suggestions, for the most part I have found Urgot to be a strong champion with a relevant kit. Just because he is found by many to be outdated does not make him or his kit inherently impotent. He primarily requires some quality of life updates to thus make him relevant for the numerous changes, champions, and reworks Riot has implemented these past few years.
As far as how he build goes, the following tends to be my perception of his core:
Usual build: 
or 
/ 
He's almost unkillable. His damage output combined with his Q poke range is stupidly powerful. But once he runs out of mana(which is often), all he can do is soak up damage.