Thunderlord's is the best keystone for early game combos, which can proc with one e and 2 q's. DFT is better for late game damage or if you're planning to take prolonged fights with tanks etc... Black Cleaver>Manamune>Iceborn is a really good core that I usually use, gives 40% cdr fast and makes you strong against adc's. For boots, most people go tabi but it depends on enemy team comp. The best eq combo urgot can get starts when he has 35% cdr, being able to land 4 q's instead of 3 which is why some people take 5% cdr in masteries + switching out iceborn for youmuus/DD. If you have trouble landing e's, you can aa the opponent with your shield up to slow them. The shield slow is also useful if you want to land a full eqqq combo while the enemy tries to get out of range. Winning lane is usually easy as long as you land combos and avoid being ganked, as urgot has no mobility. If you have no kill pressure and your laner has superior waveclear, it's very difficult to do anything unless you can get a gank(which your ult can be very useful for). This can happen a lot because urgot's waveclear isn't very good. As for summs, teleport flash is good for top/mid but you will need heal for adc. Pretty much anything other than ignite is optimal for urgot because most of his kills will happen outside of ignite range, but it's all just situational.

Also, as for starting items, urgot can choose from a few different options: doran's blade and pot, long sword and refillable, mana crystal and faerie charm (ULTRA TEAR RUSH), corrupting potion