I have a sandstone retaining wall. See picture:



I want to tidy this up as our house door opens out onto it. Because it is in such a bad state I thought that a cheap solution would be to put a carport over it and then either render, or clad the wall with stone.

I have seen on a nearby house that someone has used what looks like an exterior board to cover a wall and has then rendered it in a similar way that plasterboard is used internally. Can anyone advise me please on whether there is such a product available?
Alternatively is it a viable solution to create a lath and render structure (using wood battens) to make a firm base for the render topcoat or will this just crack the render as the wood is prone to expansion and contraction?
Any advice is appreciated.
Thank you

I've not had structural engineer out, but I've read up on this type of erosion to sandstone and I believe that it is far safer than it looks. I'm wary though or replacing sections of it without propping it which is why I thought a carport covering and render/cladding would help.