Schneider's skinks are active, ground-dwelling lizards that use horizontal space far more than height, so floor area is the single most important dimension when sizing an enclosure. An adult needs room to walk, forage, dig, and move between a warm basking zone and a cooler retreat — a proper thermal gradient simply cannot exist in a cramped space. As a general principle, bigger is better, and an enclosure that feels generous for a single adult is closer to a minimum than a luxury.
Juveniles can be housed in smaller setups for ease of monitoring and feeding, but they grow steadily and will need upgrading. Many keepers find it more practical to provide near-adult-sized housing early and simply furnish it appropriately, rather than buying a series of progressively larger enclosures. The length and width of the footprint matter most; extra height is of limited use to a terrestrial species.
When evaluating space, account for the furniture as well as the animal. Substrate depth for burrowing, hides on both the warm and cool ends, a water dish, and a basking platform all consume floor area. An enclosure that looks roomy when empty can become tight once it is properly outfitted, so plan the layout before committing to a size.