More shed-building related questions. I was planning on using
"Hardi-plank" cement cladding but on closer inspection it requires
a 20mm airgap. Which is a pain.

We've got a timber frame with celotex insulation ready to go into
the gaps. Ideally we will put a membrane over that and then
mount cladding directly on to the timber frame (through the membrane).

What are the options? Looking for low-maintenance, primarily, and
some sort of pseudo-wood finish secondarily.