Apologies for the delay in following up on my original post.
Just to summarise:
The shed is 10'x6', bought via shedmonkey.com and is their 'hipex' (high apex) product. It's built from 12mm tongue & groove boarding.
This has been treated with two applications of 'Barrettine' solvent-based wood preserver and allowed to dry before assembly.
The base is formed of 24 'Ecodeck' plastic interlocking tiles which have been infilled with 100mm gravel; although the area concerned is brick-paved, I wanted to raise the overall height of the base structure off the ground to minimise the risk of early deterioration due to rainfall 'splashback'. This gravel base has in turn been treated with three drenchings of 'Pathclear' to discourage weed growth (unlikely as that might be in almost total darkness) as well as two powderings with ant-powder. There are gaps between the base bearer timbers through which I could get a pressurised weedkiller lance in the future but throughout the project, my consideration has been in terms of a low-maintenance, 'fit once and forget until such time as I fall off my twig' solution.
The current status is as follows:
Internal ceilings & walls have had damp-proof membrane applied followed by wood-fibre board insulation then covered with every-day bubble wrap to minimise 'fibre fall-out' (the green dust from it is evil and gets everywhere if/when disturbed by cutting/stapling).
Original T&G floor has had DPM/wood-fibre insulation applied followed by 18mm MDF covered with a premium-priced off-cut of kitchen floor-grade 'lino' just to make it easy to keep clean (and find/pick up those tiny little screws that when dropped always seem to bounce/somersault three times, each time sounding as though they've landed close by - yet on the last bounce, they fly off into a random area anything up to ten feet away).
I will upload pics soon ... I promise!
Best wishes
Guy