My run started off as huge for the 6 chickens I planned on getting, now it feels a little overcrowded with my 19. However they spend very little time in the run, I let them out into the garden. It's about 30 square meters (320 square feet) in all, but that includes 2 coops, a sick pen and an old rabbit hutch they use as shelter.
To fox proof it I spent 4 weeks preparing the run before the original hens arrived. I buried vertical flagstones along the sides of the run so it has 3 foot of solid concrete underneath. If foxy can bury deeper than that in 1 night respect to him. I then put coated wire 6 inches down the concrete on the outside of the concrete and nailed it to fence posts. I also lined the edges with heavy rocks but I think this may have been overkill. Cage wire is also over the top and I have trained blackberry brambles over the run so anything trying to climb over the run gets a lovely amount of thorns in their feet whilst the chickens get some lovely blackberries in the autumn and I get caught going to lock them up at night.
Build up is scraped off when the run starts to get slippy. Frankly it's a real pain as the run is built on heavy wet clay and this forces its way up through the stone chippings I put as a base which means it needs doing a lot, even though the hens spend a fraction of their time in the run. I'm considering planting a few chicken proof plants in there just to dry the ground out so I don't have to do it every ruddy month, twice a month in winter or they'll end up with trench foot.
Bedding material is just wood shavings (bulk from the local building supplier, he prepares them for us, massive 2 meter by 1 meter bag for 99p) I've given up with flooring material, it's just one more thing to scrape out. If I could find something that isn't concrete that I could hose off once a week with the coops I would consider, but I can't. Suggestions welcome.