A small herding dog with a loud voice
Shelties are 15–25 lb and fit the 24" or 30" crate. Temperamentally they're small Border collies with a rough-Collie coat — smart, herding-driven, sensitive, and famously vocal. Barking is the single most common crate complaint with the breed, and it's largely genetic. Manage crate placement to avoid barking triggers (no windows, no doors) rather than trying to train it out entirely.
Shelties are velcro with their person and often shy with strangers. Central crate placement and gradual separation tolerance are important; harsh corrections for crate barking make anxiety worse and often produce a dog that barks more.