Justin Bieber oughta start a boy band with Lil Wayne, Chance the Rapper and Quavo, 'cause they'd obviously kill on tour ... so says Bieber's longtime producer pal.

We got Poo Bear Saturday night leaving Catch, where he gave us his thoughts on DJ Khaled's newest hit single -- "I'm the One" -- where the Biebs and everyone else hop on the track together. 

Poo thinks the song's gonna rise to #1 on the Billboard Top 100 pretty soon -- but more importantly, he says the guys should consider starting a group and hittin' the road. 

He might have a point ... who wouldn't pay to see these dudes on one stage together?