Condensation is just going to happen with a metal garden shed, especially if there's moisture at the base. The problem can be helped a bit if the shed has some insulation or was put on a sturdy base. If you're using the shed to store important stuff that can't get wet, it might be easier to get a new shed. A wood shed or other material like vinyl won't have this issue.
Garden Shed Metal Shed
Garden Shed Metal Shed