Thanks for the replies.
I've no experience of trying to make hens pay, that is true, but I've kept them in varying quantities most of my life so hopefully have some transferable skills.
As stated I'm expecting foxes to be the main issue, I've yet to see a truly fox proof chicken run especially as i want it mobile. If I was going to keep them in one spot a pheasant style pen, of which I've built a few, would be ideal. I have thought of a mobile version using heras fencing but if would still be a big job to move it so to start with I'm going to try electric poultry net I think.
The point about maintaining eggs into the autumn is a good one, luckily the csmpsite popularity tails off with the weather so the demand will be lower later in the year. I hadn't thought of that though. My previous ex layers never had artificial light and still laid pretty much into autumn if a bit sporadically.
What are people's thoughts on 25mm weldmesh for coop floors?