Why am I getting a lot of condensation in new shed?
Because the roof is metal it will get cold and when the (relatively) warm damp air inside the shed comes into contact with it, condensation forms.

You need to make sure that there is a thermal barrier between the inside surface of the roof and the outside surface.

So any of the things you suggest would do, but might cause ventilation problems (say). So a false ceiling would probably work best.