So i made a build for my favorite champion Gnar but I don't know if it is as effective as the recommended tab's build. My build is... Berserker greaves, Blade of ruined king, Phantom Dancer, Thornmail, Bloodthirsteir, Sunfire cape. I would like to know if it an atleast somewhat good build. Thanks in advance :D 
Have you tried switching thornmail out for dead man's plate? You're running a lot of sustained damage between all the items. By the choices, you do your best damage in little gnar form. The only lacking aspect is a defense to magic damage. Given that there are not a lot of AP top laners, I can see this build working very well. However, dead man's still gives the armor like thornmail, but you also get more health.
You could make that a situational item pick or permanent aspect in your build. Try it out for a few games and see how you like it.
gl hf
[slayer-jinx-catface]
build this 
Honestly, I think that your build is pretty good for one of the more damage-heavy Gnar builds. Phantom Dancer, Thornmail and Sunfire Cape all help mitigate damage done by most top laners, since the majority run off of AD scaling and some are pretty AA-heavy (hi Aatrox). Not only that, but Blade of the Ruined King and Bloodthirster help further increase survivability alongside Berserker's Greaves, since you have a fair amount of Lifesteal and attack speed - and on top of that, the Attack Speed plays in well to Gnar's mini-mechanic with Hyper - pelt enemies from a distance, score big damage, then use Mega Gnar for cleanup or the like.
If it feels effective, keep with it![slayer-pantheon-thumbs]
if you want something off meta try frozen mallet, runans, black cleaver, wits , botrk/ <random tanky item>, <situational boots> you will shred armor, mr , %Hp slow aoe and move super fast with phage :D
Go 5 Zeals and boots of mobility
