Seriously, does it have to be metal?

I ask because it will suffer condensation in November+ like an ice-
pack on a humid day. That condensation will be external & internal
dropping off the roof onto anything inside. You can insulate, but most
steel sheds are profile section so it gets fiddly. Can you not do a
wooden shed?

If it comes to it - get some aluminium angle and make a frame, then
clad with that recycled plastic "?farmboard?" cut with a plastic saw.