Metal Sheds are prone to condensation over time. This is because as the temperature outside gets colder, it affects the fabric of the shed.
Also, as the metal skin of the shed is on a millimetre or so thick and metal is a good conductor of heat, the metal will get cold very quickly.
How to help condensation reduce condensation in your metal shed
Try to keep the shed as dry as possible,usually the metal shed will have a raised floor and often it is installed onto a concrete base, before laying your base lay a moisture barrier beneath the concrete we call this a damp proof membrane, a sheet of plastic will do the trick.
The next step is to improve the ventilation of the shed at the eaves level, ventilation in the opposite wall of the shed means that if there is any breeze it will help clear the warm air.
This is by no means a cure but a prevention but will help reduce your condensation