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.