Big Daddy's garage is a garage occupied by Big Daddy and his allies in Sing. It is used as their hideout and living space prior to the incarceration of Big Daddy and the Gorilla Robbers. It also stores a black pickup truck that is used during heists.
In Sing, Johnny can be seen looking at a flier of the singing contest that Buster Moon organized and hiding it after his dad shows up, it's also shown when Johnny tells his dad that he is going outside, when he really is going to the contest.
Also, after Johnny arrives from the Moon Theater his father is with his gang members, and Big Daddy tells Johnny about a plan of robbing a ship full of gold.