MidWest Homes for Pets presents the Critter Nation Add-On Unit. Small animal owners can link an additional unit to a one- or two-story Critter Nation or 180 series Ferret Nation, the company states. The unit features an attractive gray quartz hammertone finish, full-width double doors, a wide expanse shelf, a removable plastic pan and two ramps with reversible fleece covers, the company adds. The unit measures 36 in. x 25 in. x 241/2 in.