Introduction:
The main requirements for housing all kinds of poultry is that they are protected from predators; the weather; have adequate ventilation, constructed out of materials that will not harm the birds, and that the house is easy for the owner to use. The prime concern at all times must be the welfare of the birds.
The precautions you take against predators will depend on what is prevalent in your area. Increasing parts of UK are home to foxes and other predators which have become much bolder and can be present in the daytime. I know of people who have had birds taken from their garden right under their noses literally. This is when electric netting is so very useful.
If you need to provide shelter from the weather, or temporary security occasionally, then its great to have a house and run like this:
A Grosvenor house and run.
OR
An Aylesford house and run.
The Grosvenor illustrates several useful features not seen in some houses - the house is raised off the ground which keeps the birds away from rodents if the latter are a local problem. It also means that the ground beneath is available to the birds and the grass is not killed off by the pressure of the house. It provides an area of shelter and somewhere for the feeder to be put in the dry. There is solid panels to protect the birds from the wind and rain, which also means they do not have to go into the house - so reducing the mucking out that is needed.
Both have external nestboxes for chickens - this means that is is very easy for you to collect eggs and more space inside the house is available to the birds.
The Aylesford is good for a few ducks as it is at ground level - for ducks the nestbox is unnecessary as they do not use them.
At the end of the run of both is an end release panel - this allows you to let the birds out to range around your garden, either free range or protected by an electric netting fence.
As these sort of houses can be moved pretty easily they are very useful to include in the rotation of a vegetable plot. As you dig over a bed - put the house over it so the hens will work it over; eating all the grubs
and bugs; manuring it and working over the clods. They will enjoy cleaning up after crops: for example beans and peas - which you can them dig in.
If your space is limited and you feel that you are likely to end up with simply a mucky poached bit of ground, then what you can do is create a bark pen and move the birds over this. They adore raking around in the bark which will be home to lots of bugs. You can scatter grain in the patch they are about to use - which will germinate providing fresh greens.
Every so often - depends on the thickness of the bark; the porosity of the ground; how many hens; how often they are moved; etc; the bark may need to be removed and replace. It will be a very good mulch for any garden if put in a pile for a while to compost further.
If you are lucky enough to live in a dry area with well drained soil and keep the bark well turned over between use then this may only be once a year.
The other advantage of a run either attached to a house or free standing is that when you go away you can safely leave them enclosed and the family member or friend, who you bribe with fresh eggs, to look after your babies will have less responsibility in that the birds are safely confined and just need fresh water and feed every day.
MINK and PINEMARTEN: If you have a flowing stream / burn through your garden or close by in some parts of the country you may have mink in the area. If you have coniferous woodland around you then in some parts of the country you may have pinemarten. These two are the worst predators, slaughtering wholesale if they get in and need special provisions.
There must be no way for them to access the house and they can get through gaps smaller than an inch. I suggest to people who buy one of the houses that doesnot have a timber hinged roof to put 1/4 or 1/2 inch weldmesh underneath the Onduline.
Houses that have an Onduline roof without a timber backing cannot have the corrugations blocked in or the essential built in ventilation would be badly affected.
If they have a fixed fenced run then I also suggest that they do the same to the outside of base of the run to prevent them burrowing underneath.
BIRDS OF PREY: We have a variety of birds of prey here in the West Coast of Scotland but have been little bothered by them. If in your area there are reports of attacks then either a house and run or a covered larger pen is necessary. We have found that netting for raspberry cages works well.
Covered runs are most important when you have chicks outside with their mums. Crows and gulls will decimate the clutch in very short order. For a broody a house like the Hereford
is ideal, providing a generous space for them to grow up in, and easily protected from the weather.
If you have the space to have a number of birds then a larger house is more useful. 
This can be pretty simple in structure needing easy access for the owner - like the good sized door in the Westford above for cleaning out; a pophole for birds to go in and out; good ventilation - in this house it is provided through the corrugations of the Onduline roof.
This is ideal for geese and ducks - without the nestbox shown here; for geese you can use the larger door for them to go in and out which they prefer.
It has a solid floor. We use a few slates and some Damp Proof Membrane to level a house in its position and protect it from the moisture in the ground so extending the life of the base.
This size of house (approximately 4 ft
by 4 ft) can be fitted with carry handles on the side making it easy to move around if the ground in front of it gets mucky. The other option if it is to be sited permanently is to put down a sheet of ground cover membrane and then a layer of gravel before installing the house. This is easy to rake over and can be replenished if it gets mucky, especially around the door.
Houses like this can have a free standing run, which can be useful if you need to enclose them for any reason - using a bit of ground that has special plants nearby; when some one else is looking after them; or you want to separate one part of the flock from another.
For chickens you will need the roosting bars and the external nestbox.
Roosting bars can be around a foot to 18 inches off the ground for medium and light breeds, but the larger heavier breeds like Orpingtons; Jersey Giants etc need the perches lower as they don't like to drop down and getting up can be more difficult. However they MUST be off the ground, its very poor design and worse welfare to have little slats in the floor where the birds cannot perch properly but are just lying on their keels on the ground.
The bars should be about 2 inches square with the top bevelled off to create a good gripping surface. It is preferable to provide about 18 inches length for each bird - if you have space 2 foot for the larger breeds. Bantams and the smaller medium weight birds will be happy enough with 12 inches.
The nest boxes need to be around 12 inches square for small to medium chickens, 15 inches for the larger breeds and turkeys prefer one aruond 18 by 24 inches.
One section for each 5 to 10 chickens is ideal. For example if you have 12 - 15 hens then 3 nestboxes is good; if you have 50 - 75 hens then 10 is fine.
BIGGER BREEDS - A larger house is also vital for the bigger breeds - coops that are only around 30 inches high are really rather low - especially once the birds are up on their perch. It is best to avoid having the birds heads up near the ventilation or respiratory problems can easily occur.
If you consider that the bigger breeds are larger in all dimensions it becomes easy to see that the figures given for house occupation will have to be adjusted. This goes for ducks - where they will need greater floor area and chickens - where they may need larger nestboxes; taller housing and more perch space.<
Lighting:If you want eggs all year round you will need to investigate providing light to the house. If you have pure breeds then they naturally have a shorter laying season although some strains may be good winter layers.
The commercial birds, such as the Black Rock, will respond well to increasing the light in the winter. A 14 hour day is necessary for strong egg laying and using a low light and a timer will simulate nautral daylight.
The Brentford poultry house for up to 24 birds.
Ventilation : To prevent respiratory problems and the build up of condensation and bacteria it is vital to have good ventilation in the poultry house, but not drafts. The best place at the top; it should be covered in wire (weldmesh is best). Glass is rarely suitable in a coop of any kind, it can break causing a hazard and no species want to be hot and light in their houses. It is vital that the birds when roosting do not have their heads in a draft. For larger coops it is a good idea to have a sliding wooden window so you can alter the level of air - as in the house above. It is not good idea to have an overly insulated house, healthy dry birds do not need heat, and plastic housing creates a stuffy environment.
Flooring : A solid floor to the house is the best for the birds. They need a generous area of shavings to soak up the dampness from the birds as they come in and out in our variable climate. some people like using droppings boards beneath the perches to keep some of the muck from the floor. As we are in a wetter part of the world and the birds use their houses alot during the day in showery times we prefer not to use them as they can make much of the available area to the birds rather dark. We have to top up the bedding in the houses most days anyway.
What size to get : THE BIGGEST YOU CAN AFFORD - I really mean this. If you can afford to get one that is big
enough to give the birds around 1.5 to 2.5 square foot floor space each; plus space to put a feeder of the apporpriate size and waterer then your birds will be able to use it easily when the weather is wet; snowy; very
hot etc. The bigger house will also mean that you are not having to clean it out every five minutes.
