Height of parapet on pitched roof shed

Having your block built boundary wall as one wall of your insulated shed is a terrible idea. Making it 3.2 metres high is even worse.

Rain on the other side of the block wall will soak through through the blockwork like a sponge, and into your shed. Which will make your insulation useless (possibly worse than useless). Even if it's adequately rendered on the other side to keep the rain out, there's almost certainly no DPC (a separate damp issue), and the foundations are unlikely to be adequate for a 3.2 metre wall Vs the current 1.8 metres or so (more weight & more wind..) which raises serious safety issues.

Also, if it's the boundary wall, it belongs to both property owners. So the (current or future) owner of the property on the other side could object to the 3 metre high wall (which would need planning permission- exempt height of a boundary wall is 1.8 metres). They're also entitled to do what they want on their side including (for example) building a raised bed, which would definitely cause damp issues in the shed.

It would also probably cause potential issues when selling the property (planning, plus lack of clear documented consent to build on the party wall).

Most if not all of these issues can be eliminated by building a new wall set back maybe 500mm from the boundary wall and building a new wall with appropriate foundations (and external render).