Contrary to wooden sheds, metal sheds do not require sanding or pest control. The only maintenance issues are rust and corrosion, and there are some preventive measures you can take, such as applying a protective layer of paint with anti-corrosion elements followed by a rust-inhibiting finish. Repeat the process every few years.
However, when purchasing a metal shed, make sure it is rust-resistant and comes with a warranty against rust. Metal will not distort or warp under different weather conditions, and it is possible to reinforce it against strong winds.