Hi Annie
Dick M has the right idea - make them work! :lol:
I'm a builder (almost retired
), I've built lots of sheds over the years but never converted one with a metal roof. Do have a large plastic storage shed that exhibits the same condensation issues however and I have converted several of barn / stable projects into habitable dwellings.
Spray foam. - Horrible stuff to apply but it works well. I would question any possible DIY application and I've only used it once when I called in a specialist company to seal the slated roof of a grade 2 listed stable. You can't get a flat finish but for your roof it would be excellent if expensive.
However: i would start with the roof, fit a framework and insulate with cellotex, thicker the better, a membrane and face with plasterboard, OSB or ply.
Next for me would be the floor and you would need a DPM to stop damp, lapped up the walls then either put in a floating floor of V313 T&G chipboard or 18mm ply on top of cellotex or polystyrene slab insulation, 50mm minimum. Otherwise timber joists with insulation between and c/board or ply over.
I'd do the same with the walls and frame with 4x2, 3x2 or 2x2 but use a breathable membrane instead of DPM, (assuming the walls are timber) and use OSB / ply so you can hang stuff on the walls. Painting the walls and ceiling white makes a huge difference.
an alternative to cellotex or polystyrene are cavity bats which are slab glassfibre sold to insulate cavity walls whilst building. common thickness of 50mm, 75mm and 100mm. I doubt it would be much cheaper than cellotex, especially if you source seconds on the net.
There are lots of threads on shed building Annie and most of the basic principles apply whether converting or scratch building and I would add that my suggestions are not necessarily what others would recommend so read them all and pick the bones out to suit your own needs and pocket. :wink:
cheers
Bob