Stable floor conversion

[rs6mra]

I am planning on converting an old stable block to a workshop.
The floor is currently cobblestone and I’m thinking the way forward is to apply a dpm like the ones used below a course of bricks. I’ll then rest 4x2 on this and then level if off, PIR insulation and then plywood.
The stable block is flanked by 3 brick walls and the plan is to have a a single course of blocks at the front and then a timber clad wall on the left and door on the right.
Your thoughts on the above would be most welcome

 

[Pabs]

I've done similar in an outbuilding but laid a floating floor.

iirc was Hardcore/ sand, membrane, polystyrene rigid insulation then chipboard