It is not recommended to keep a gerbil in a shed outside.
Sheds can become extremely hot in summer and very cold in winter, and gerbils are sensitive to temperature extremes. They are also vulnerable to predators, parasites, rain, wind, and security risks.
The best environment for a gerbil is indoors in a temperature-controlled space with a secure, spacious cage. Even with insulation, predator-proofing, and weatherproofing, keeping a gerbil in a shed remains risky and is not advised.