We're loking to do just the same! Don't forget the foxes! You need a six foot fence (at least) to keep them out, and badgers will come underneath.
Here is some more info from
The Battery Hen Welfare Trust:
CARING FOR BATTERY HENS
This information has been designed to help owners, who have not had spent battery hens before, understand their needs and how to care for their new girls. We dont claim to be expert on hens - there is plenty yet for us to learn - but this is just some simple guidance, which we hope may be helpful:
Accommodation
When choosing accommodation number of hens and space available are the key issues.
The henhouse needs to be sturdy and secure to protect from fox and badger.
When selecting a house we advise you buy one to accommodate more hens than you actually intend to keep. For example, if you want six hens, we would advise you purchase a house to accommodate at least eight hens. This will ensure they have plenty of space not only to roost and nest, but also to take shelter from the weather during the day.
There are houses which are static with attached runs and others which are movable. You will need to assess the best option for you taking into account that hens like to peck and scratch grass - the bigger the run you can give them the better, not only for their own enjoyment, but also to keep the ground they are ranging in good condition. (Hens like to create dust bath areas which will become mud baths in the wet weather). If you decide to select a house you can move regularly and free range the hens you will need to ensure that the hens are well homed before allowing them complete freedom.
Many people choose to adapt a standard garden shed with perches and nest boxes. As a guide a 6 x 4 shed will comfortably accommodate 12 - 15 hens.
Bedding
A number of products are commonly used on the house floor: chopped straw can be used for larger numbers of hens and shavings for small numbers. If you are using shavings it is important to buy first grade shavings with the dust extracted. This is available from most country stores and comes in bales.
Nest boxes ideally need some soft material in order to make a cosy place in which to lay an egg. Shavings with some hay on top is a good option, although this can sometimes be a favourite hiding place of the red mite (more on bugs later).
Daily Routine
Hens like to be up early, so as soon as is reasonable let the girls out.
They will need fresh food and water and will want clean nest boxes to lay eggs in. (Some houses come with nest box lids that can be closed at night - this is very useful to stop them sleeping and fouling the nest - something battery hens are rather fond of doing).
The hens will go about their business during daylight hours and will rely on you to close down their pop holes at night for security.
It is advisable to keep the ground as clear as possible of spilt grain and other food matter as this will only encourage the local rodent population to move in! If you have the space it may be wise to feed inside the henhouse.
Life Expectancy
It is very important to be aware there is no guarantee how long a spent battery hen will live. Some may only live for as short a time as one week; others 8 years plus. On average most live for 2 - 3 years.
We believe that if they are lucky enough to enjoy scratching around for a week or so - hopefully with the sun on their backs - then they are luckier than most battery hens.
General Fitness
Your girls will, of course, have done nothing other than stand in a tiny cage for their entire lives. Consequently they will be very unfit to begin with and usually completely unable to jump up to a roost or nest box.
This problem can be overcome by placing a ramp up to the roost/nest box or giving them access to a nest box on the floor (even a cardboard box on its side with shavings and a bit of hay in will suffice until they are fit enough to use the proper facilities). It doesnt take them very long to build up their strength and within a couple of weeks most are capable of jumping to a standard roost height.
Cockerels
For the same reason as above, we always advise that it is best for the girls if they are kept separate from a cockerel for at least a couple of weeks - (a) theyve never seen a cockerel and its a pretty scary experience when they do and (b) if hes big and keen, he may do damage by jumping on a hen with weak legs and/or bald backs. If you can, give them a couple of weeks to build their confidence and strength.
Health
We never knowingly allow a hen to go to a new home with health problems, although occasionally one does slip through the net because of the large numbers we are dealing with.
When the hens first go into the cages they will have had a long list of vaccinations to protect the farmer against large losses. These are usually administered through spray misting the chicks or in the drinking water. The most common diseases vaccinated against are Mareks disease, infectious bronchitis, salmonella, Newcastle disease, Gumboro disease and epidemic tremor.
One of the more common problems with spent battery hens is bruising, often to legs, sometimes to wings. This usually occurs when they are removed from the cages and can be so bad the hen finds it painful to stand. If you gently look you will see dark bruising under the skin and arnica cream rubbed in works wonders. As long as you see that she gets food and water, a bruised hen will recover within 7-14 days with no lasting ill effects. (If possible, do not separate her from the other hens, as when you return her to the group she will be seen as an outsider and bullied).
Occasionally, a hen will have a broken bone and in this instance it is advisable to ask your vet to set the bone - wings and legs can be mended quite successfully.
Weather Conditions/Temperatures
The hens have been used to very warm conditions within the battery unit; this is why so many have large, floppy combs (they act as heat dissipaters) - the combs will not only redden as they are exposed to the weather, but usually shrink as the hens need to lose less heat.
Obvious precautions need to be taken - if the sun is very strong the hens can suffer sunburn, especially the oven-readies. Equally if its really cold, wet and windy, they will initially need to be encouraged back into their new homes otherwise they tend to just stand still and get wet - this in turn can lead to sniffles and worse.
Homing the Girls
When you first take your girls home, its usually best to keep them in the house for a day or so to home them. Even the pleasure of discovering a shed is far more stimulation than they are used to, so they should be quite happy. (If you have a small enclosure restricting their range, then it would be ok to let them out straight away).
When you let them out for the first time, let them out about a hour before dusk which will encourage them to stay near to the house and return as darkness falls.
Egg production/nesting
Although there is no guarantee of how many eggs spent battery hens will lay, generally you will get about a 40-50% production rate, ie 10 hens will lay 4-5 eggs daily. THIS IS A GUIDELINE ONLY.
Battery hens have absolutely no concept of a nest box facility. You will find eggs will be dropped wherever they happen to be walking at the time of lay. Rubber or china egg balls are a wonderful way of teaching the hens about the pleasure of laying in a cosy nest. They can be quite clumsy to begin with and the rubber eggs are ideal because theyre realistic and indestructible!
Nails & Beaks
Toenails are often very long, although a new regulation now in force stipulates that cages should have a claw shortening device. They will often wear down quickly as the hen free ranges, but occasionally they are so long they will distort how the hen places her foot on the ground. We do try to clip as many as we can, but if we havent had time to clip the nails, and they are too long, dog nail clippers will do the job. Always take care not to cut the quick.
Beaks have nearly always been debeaked; it is the top beak which is cut, making the bottom beak very often look like a shovel. DONT be tempted to trim the bottom beak, in most instances it will wear down to its natural size and shape whilst the hen free ranges. The hen will cope with what she has, after all shes lived for a year with the beak.
Food & Water
Battery hens have been fed dry layers mash throughout their incarceration in cages - they know nothing else. We strongly advise that at least to begin with you continue to feed layers mash and offer alternatives gradually if you want to change their diet.
Layers pellets is the same as the mash product in pellet form - however, the hens dont recognise the pellets as readily and again we strongly recommend you feed mash at least to begin with.
It may also be worth noting that dry layers mash will take on the mantle of comfort food to a hen which may be off colour. In more than one instance feeding dry layers mash has turned around a lacklustre hen.
Establishing the Pecking Order
Youll probably find the girls will be in total awe of everything around them for the first few days and they will be very polite to one another. However, once they get the hang of the daily routine, usually within 2-3 days, they will then start to squabble. You really have to let them get on with it, they are merely sorting out the pecking order, ie whos going to be head of the household. Try to observe that all the hens are eating and drinking and that no blood is drawn! If blood is drawn, youll need to separate the hen as the others will only continue to bully her.
Youll most likely find that it is the smallest, most feather bare hen who causes the most disruption, having at go at anybody and everybody. Please understand that this hen is only behaving as she is because shes probably had to fight for every mouthful of food and water within the cage and every time shes managed to get some, someone behind her has been having a peck at her - hence her threadbare appearance. It will sort itself out in a couple of weeks and the most disruptive hen will realise there are far more interesting things to do rather than worry about her position within her new family.
Bugs
The most common problem you can import when you take on battery hens is red mite. This is a tiny mite that feeds on the hens blood at night and then during the day lives in the shed - usually under perches or in the nesting area or simply in cracks and joins in the house.
It is something which can be controlled with many products on the market and like fleas will flare up in the warmer weather and die down during the winter months. It does not usually prove fatal to hens, though in extreme cases if left untreated can cause death.