For my first build, I decide to make one about my main,urgot. Urgot is a very good ad carry and harasser but he is a little bit hard to play. But with some practice you will became legendary.You can play him mid or bot.At my opinion, he is better bot with is great harrassement. I hope you enjoy :)

Pro: A good harrasser, he have a good slow when is shield is active, good damage, his ulti his a good engage
cons: a little bit hard to play, need a lot of mana, need to be a good skilshoter if you dont touch anyone with noxian corrosive charge

with urgot, you need:
1 spell to escape teamfight easily and for chasing; you have flash or ghost, personnaly i use ghost because its a lot easier to use
for the second spell you have a lot of choice; exhaust, ignite, teleport, cleanse, heal,
you dont really need clarity, you will be ok with your munamune

for masteries, I go for ad one. I pick attack damage, attack speed, life steal, armor penetration, attack damage per level, critical damage, damage dealt and some armor and magic resist. If u dont want to buya munamune, you cant pick mana and mana regeneration masteries.

For runes, I pick greater quintessence of desolation so i can have a lot of armor penetration, i pick greater glyph of wrading so if u mid you will have more survivability, greater seal of replenishment to be sure to have enough mana early game and to not have to back for mana and finaly, greater mark of desolation for more armor penetration. You can pick as well greater seal of resilience if u are more laning bot vs ad carry.

the principal utility of urgot ulti is for engage team fight. you can target ad carry bringing him to your team and then you can flash back to your team geting an easy kill. You can also use his ulti when you are getting tower dive. that will make the tower diver getting hit by the turret multiple times and then he will be slow. you can then attack him to try to kill him or just run.