Garden shed / DPM

I'm looking to build a shed / workshop in the garden, but trying to do so out of as much free/upcycled materials as possible. Most of the timber I have is untreated and insulation is fibreglass and was wondering about dpm under floor.

Timber used for the floor joists will need protecting from damp and the insulation will need something to hold it in place (and prevent mice etc getting at it?). I was wondering if effectively wrapping the base in damp proof membrane would work? (all the timber would be protected from damp and the dpm would stop the insulation falling out of the bottom).

Rigid insulation would work better, but as I don't have any at the moment wondered if this approach would be ok, or am I missing something that will cause a problem later?

Excuse the basic drawing, but something like this image?

Appreciate this wouldn't be the normal way of doing things.

Without ventilation, there's a good chance your rockwool type insulation will get waterlogged (from condensation that has nowhere to go). If you can create an air gap between insulation and dpm (support insulation with chicken wire?) And arrange some drainage holes in the dpm, you should get round that issue.

Thanks, I was forgetting about any condensation between. I'll have a ventilated void under the floor anyway - perhaps chicken wire + dpc under the joists will do anyway and I'm worrying about mice etc too much!