Females in a group, or one male alone
A mouse's first home is shaped by who lives in it. Female mice are social and should start as a small group of two to four from the same litter or already housed together, while male mice are territorial and are usually kept singly, with extra furnishing and human contact making up for the missing company. Whichever you choose, the enclosure should be a glass tank or similar solid-sided home with a fine mesh lid, because mice pass through bar gaps that contain a hamster and chew steadily at plastic bases. Depth and cover matter more than height. A mouse crossing a wide open floor feels exposed to predators, so the goal is a tank where a mouse can travel from the water bottle to the food corner almost entirely under or behind something, using ground-level routes rather than bare crossings.
Deep bedding and a maze at ground level
Fill the base with a deep layer of plain, unscented paper or aspen bedding for digging and nest building, and add a heap of soft hay or shredded plain paper in one corner. Mice build elaborate, domed nests and will haul bedding mouthful by mouthful to the chosen spot, so let the first nest stand rather than tidying it away at the first spot-clean. Now clutter the floor deliberately: cardboard tubes and small boxes linked into runs, cork and wooden pieces to climb over, a small hammock or fabric pouch hung low, and ropes across one end for the mice who like to climb. Rotate one or two pieces at each partial clean so the layout stays interesting without the whole scent map changing at once. Provide a hide per mouse plus a spare, just as with larger small pets; a group that can split up sleeps more peacefully than a group forced into one house.
Small wheels, scattered food, and a low bottle
Fit at least one solid-surface wheel sized for mice, and two if a group shares the tank, because a single wheel in a group becomes a queue and then an argument. Keep wheels on the bedding surface or a low platform rather than raised, and clear bedding from the runners during spot-checks. Scatter a mouse seed and pellet mix through the top of the bedding daily instead of using a bowl for the whole ration, so feeding becomes searching, digging, and carrying, which is how mice naturally spend their waking time. A tiny piece of plain vegetable or a seed offered from fingers at the tank side makes taming progress quickly, especially with a lone male. Fit the water bottle low, check its tip daily, and use a heavy miniature bowl as backup if a group is sharing one spout.
A calm room, gentle cleaning, and taming by hand
Place the tank in a calm room out of direct sun and away from scented sprays, busy kitchens, and the cages of animals a mouse would count as predators. Mice have a strong sense of smell and mark their home, particularly lone males, so resist deep-cleaning the whole tank at once; clean in sections and return a handful of old bedding and the intact nest where you can, or the mice will re-mark everything overnight and the smell you tried to remove comes back stronger. Tame by resting a hand flat in the bedding and letting mice investigate and climb, never by grabbing from above. If a planned layout still leaves you unsure about cover or occupation for a lone male, put a follow-up question to KinsLe's Kimmy; she answers using the KinsLe Answers library.