Hi there ,
we had a small run in the garden and we modified a 'lads shed' from B&Q for them to roost in. It was only about 1m x 1.2m but big enough for a perch and a staw filled veg box on the floor for them to lay in. The run was just fenced off to a height of about 4 feet and was about 25 square meters. 3 hens soon turned it into a mess. We put down cheap bark chippings to freshen it up now and then, but I was a little concerned that over time there would be a build up of parasites on the land. We were tempted to let the hens into the rest of the garden, but they dug up the flower beds, and once they have been allowed out they tend to want to get out, whereas if they've never had a taste of freedom they don't miss it!
We have moved them altogether now as we managed to buy a small holding. We have had hybrids and pure breeds and I think the hybrids are hardier and better layers, they also tame easier. Your basic brown chuck will be fine. In winter we did get rats coming in for the feed, we now use a treadle feeder so that the rats can't get to the food, it's worked so far. Good luck, don't be put off, they are delightful to watch scratching about and once you've had eggs from your own hens you wont ever want to buy any again!