Building a fixed run - best floor covering?

[Cakehead]

We've had an Eglu the last few months and have really enjoyed having the chickens. However, we now want to build them a permanent base in the garden, so we're not moving them around throughout the winter. What's the best thing to put on the floor? I've read shingle is good (that was in Poultry Keepers monthly!) but how do you keep in clean? And are you mean to put a concrete base underneath it? And if you have woodchips, how often to do you have to change them? What have others used?

Considering chucks are jungle fowl they will want to scratch about for worms etc, have a dust bath, pick at grass etc so I can't understand how concrete or shingle could possibly be good. Chucks foul areas quickly and get worm infestation if the ground is not changed regularly.

It would be a devil of hard work to wash off shingle/gravel unless you scooped it all out to dry.

Surely changing the area they peck at/defecate in regularly is best?

My permanent run is on concrete slabs, which we cover in hemcore (horse bedding stuff). The chooks love scratching about in it, it soaks up the poo and masks the smell, and is relatively cheap. I change it every 3-4 weeks, and it composts well. I prefer to use something which can be totally and cheaply replaced, rather than trying to clean something like shingle tbh. However, my girls free range for hours a day, so they're not confined to the run, which might make a difference.

I've found a deepish layer of hembiose on concrete flags fine for the months when the grass isn't growing.

we have bark chippings over a weedproof membrane, with sand underneath.
they love it, have not had it long, am picking up as much poos as possible, hoping rain will deal with the rest.