Champion idea
Champ has a 7th item slot
Sometimes when he kills minions and always when he kills a large jungle monster he receives 1-10 soul shards(based on game time min at 1 minutes max at 30)
He can use the soul shards to create a special 7th slot custom item by choosing out of 3 base items for example "Avarosa's frozen bow passive:+100 attack range and attacks have a 10% chance to stun for 0.5 seconds"
and 3 stat blocks with random stats like 25 ad,25 armor,100 hp or 30 ap,40% attackspeed,20 movespeed and you can choose one of those
The tiers of spirit forged items increase with game lenght at 5 minutes you can craft tier 1,10 minutes tier 2,15 minuter tier 3,20 minutes tier 4 and 30+ minutes tier 5(the best tier) unlocking more potential base item options(at tier 1 you will roll from tier 1 pool,at tier 2 time you will roll from tier 2 pool etc.) and bigger stats
The price also increases increases with tiers a tier 1 item only costs 10 soul fragments and a tier 5 item costs 250
You can have only 1 spirit forged item at a time the last one will be destroyed and replaced by the new one.