Solid bronze coloured polycarbonate?
Anodised ally colour (assuming someone does those sorts of sizes)?
Hammerite copper paint does look like copper?
Gild with copper leaf?
Thin copper sheet sandwich over something?

pgk

If that windbreak is not in a very sheltered position I think I would use 40mm box section for the frame rather than 25mm. There's quite a square footage of screen/sail there which could buckle the frame in a storm.

re. the finish, If you used aluminium sheet, you could get it treated with a translucent copper powder coat like this: weblink which should give an approximation of clean copper without the eye watering cost.

A house in the village has a fence made of pierced steel sheet which I think must be the type that Michael suggests, It has "rusted" to a nice reddish colour. We also have a garden ornament made of something similar which looks nice.

Composite fence panel possibly see ** My Modern Garden **

Weathered steel ** Corten Garden Products ** from BuyMetalOnline.co.uk

Cheapest route would probably be to use a sheet of OSB and paint it! Should last 10 years or so.

John

Edit: add link

Edited By Journeyman on 01/10/2021 10:15:48

Tricoya waterproof MDF would probably do the job. You could finish it in almost any way you like.

Martin.

And another vote for ACM sheet, but would opt for 5mm rather than 2 or 3mm. Depending on budget, you can stick printed vinyl sheet to it, or even have it printed on directly. Unfortunately sheet they use at work is in short supply at the moment, and the prices keeps rising.