that's a little small for when the bp is an adult. mine is 12" deep x 12" tall x 30" long and even that might be a tight fit when my bp reaches adulthood.
they really don't need the height, as they're not good climbers. they need floor space cuz that's where they spend all their time...
an 18" tall x 18" deep x 36" long is a good size for an adult, i think that's what the caresheet says.