All unconventional builds are hated by the community, but some of them are actually quite viable. I've noticed that when you use an unconventional build, your team will generally do more poorly and not play as well as they should since they will not take the game seriously.

There are two builds that I play that I quite enjoy that I always end up with a decent score as-

AD Malz- Void Minions stack off AD, you can easily shut down an enemy carry, though he has a con with maneuverability this can be offset by building him tanky with Mercs, Manamune, Brutalizer and Atmogs.

AD LeBlanc.. A hilarious champion especially with the new changes. Built as an AD Carry she has amazing maneuverability, her stats aren't too bad and it's hilarious when you jump over three walls to kill someone with your auto attack. LeBlanc has lots of potential which people overlook.

What are some off-the-wall builds that the community has enjoyed? I would love to see the communities build ideas for viable unconventional builds.

Tanky On-Hit Lulu. Because what else are you going to do with that passive?

AP Taric. "Oh look there's the support all by himself mwahahaha free kill for m- OH GOD THE PAIN"

There's tons of builds that work.
There's less of that that are actually viable.
And there's only few, yet undiscovered builds that are available to a limited few that are legit.
Which ones you want?

My personal favourite would be a carry assassin Hecarim.

AP mundo.
Tiamat Malph.
AP malph
AP amumu
Max Attack speed Cho
AP Naut
ADC nidalee

For the truly hardcore troll, AP Garen.
Dat scaling op.

But anyone with long range and cc can work as adc.
Anyone with AP scaling can be played AP. (Like shen)

Anyone who is renowned for being squishy can be played tank. (kinda funny, dosen't work too well)

all Tanks works, try and win as early as possible.
5 people with healz works, poke down towers and get a soul shroud.
5 assassins works if everyone can get supa fed.
5 people with traps works. (Haven't tried) Nid/Cait/Shaco/Teemo/Mao? Map control OP

More Viable comps,
Poke comps
AoE comps
Early game comps + one lategame carry
lategame comp
Supression ult comp? (Skar, WW, Malz?) QSS op
The Not-Quite-Global team. Karth, Panth, GP, Ez/Ashe and Shen support. Tf works also.

AP Soraka is horrifying.
STARCALLSTARCALLSTARCALLSTARCALLSTARCALL
Oh hey, where'd my MR go?

AP Tank Kat
Lifesteal Tank Fiora
AP Jax
ASpd Vayne
AP Tank Soraka

They work, but they're always dependent on the situation. In most cases, a standard build will work just fine.

Crit Fiddlesticks
Tank GP
AD rammus
AD janna

ADC Kennen

Apparently, he's easier to play than AP mage Kennen. Although probably not as much burst damage, I don't have worry on trying to land my Q on-collision skillshot and takes advantage of his W and E instead.

I won many games using ADC Kennen, although I do have some losses, but mainly on things that aren't in my control (other team members calling me a noob, unintentional feeding, verbal abuse, people hating me playing him as an ADC Kennen, etc) or those that are in my mistake (e.g. bad positioning).

Tiamat stacking on Fiora with a bloodthirster is incredibly powerful, try it sometime if you have a good start

Only 2 "unconventional" builds work regardless of elo and team comp in my experience

Hybrid Lulu: Ginsoo's, Merc Treads, Gunblade, Trinity, Stark's, Rylai's
On-hit Soraka: Manamune, Malady, Sorc Boots, MBR, FM, Ionic Spark

Lulu is the most adaptive champion in the game, hands down, no questions asked. Her kit is diverse enough to synergise with whatever crazy build you might come up with. Hybrid build works wonders because she can just steroid herself defensively so that she can last long enough to tear up the enemy.

Soraka's starcall reduces magic resist, so building a kit revolving around this works wonderfully. Shred your enemies resistance so that MBR is dealing Pure Damage %health. Steroid yourself to outlast the enemies' burst and then calmly dismantle them with bananas.