Shed floor DPM ?

[gingerneil]

I am building a playhouse / shed in the garden - about 2sqm. The base is constructed using 2x4 treated timber, lifted up a little (~2 inches) on legs of 2x4 to raise it off the slab patio that I am constructing it on top of. I have boarded the floor area with 18mm exterior ply, screwed to the 2x4 using galv decking screws.
I have had some good responses to other questions, and have built the wall frames and roof trusses using treated 3x2. I am almost ready to screw/nail it all together to form the overall frame.
However.... before I do..... I am wondering about a DPM and insulation for the floor. Could/should I lay a DPM sheet onto the ply, build the frame on top of this, and then fold it a few inches up the frame and fix ? I would then lay 3x2 inside the frame on the floor, nailing to the outer frame to maintain the DPM and then waterproofed T&G ontop of this - maybe with some rockwool underneath.
Does this sound like a reasonable plan ? Could I use roof felt underlay for the DPM as I will have some spare from wrapping the outside before cladding?

 

[Pigeon85]

By all means damp proof the floor with what you have spare or even give it a paint but it shouldn't be a problem as long as water can pass under it and not get trapped, just 1 tip from me would be to put plenty of screws in the floor to stop any warping that may occur. Apart from that it sounds like you have it all under control