The Lemon Fool

I have a staircase that runs from my garden to a home office above the double garage. It's made of hardwood, probably Iroko. Unfortunately much of it is in perpetual shade and never fully dries out, so rots. Repairs have extended its life but that can't continue. So I'm looking to replace with something more durable.

Does anyone have a view about the relative merits of galvanised steel and aluminium or any recommendations for firms that do a full supply and installation service, either nationally or locally to me (close to M25 J6)? And are there any alternative options such as composites?

Quite a few small external staircases in Plymouth seemed remarkably similar to the ones fitted to Princess yachts. Polished stainless handrails and composite steps.
Otherwise galvanised steel mesh like on many fire escapes is a good long lasting option.

Can you not fit one within the garage so as to avoid the problem?

Dod