Thanks for the info, still mulling over for the best option, ideally I'd move it about, but space, level land and bouncy goats limit those options.
The hens are welsummer x, small up to some I've had, but I think they would get bored so I would probably let them out most of the time, unless I was going to be out until after dusk.
they currently sleep in (2) 4ftx 2.5ft weldmesh cages, raised off the ground so they have a 'downstairs', trouble is they are in the polytunnel, I really want them out.
I'm hoping it would be secure for leaving them loose in it overnight, rather than fastening them in the cages, or thinking of putting one of these cage units in there, they like to sleep right on top, not safe in the poly.
The panes we rescued I was thinking about putting round the bottom (I meant one row high), and perhaps a lighter material (perspex or currugated tim?) over the top.
good point about the floor, and OH is quite useful so he could make extra bracing if needed. I think it would be bolted down somehow, maybe to concrete flags.
still thinking, too busy with other things to get on with it just yet anyway, but the idea is slowly coming together.