To create a comfortable nesting area for pet mice, you can start by providing a suitable enclosure, such as a glass or plastic tank with a secure lid to prevent escape. Line the bottom with a safe bedding material like shredded paper or aspen shavings. Include nesting materials such as untreated paper or hay for them to build their nests. Add a hiding place like a small cardboard box or a tunnel for them to feel secure. Make sure to place their food and water in easily accessible locations within the enclosure. Additionally, provide items for them to chew on to help keep their teeth healthy and prevent boredom. Regularly clean the nesting area to ensure a clean and hygienic environment for your pet mice.