broody hen cage
If you keep breeds  of chickens that are prone to go broody then it is a good idea to have a broody hen cage.

broody hen cage design
Photo of my broody hen cage with water container andfeed dispenser.
My broody hen cage.  The water container and feed dispenser can be seen on the left.
A broody hen cage is one with wire on the floor and at least three of the sides. 

It should be suspended above the ground so air freely flows under and through the cage but it also should be protected from the weather and shaded from direct sunlight.

Place water and food containers inside the cage, preferably tying them to the side of the cage to ensure that they can't be accidentally knocked over.

It should be big enough to hold two to three hens as you may get more than one hen going broody at a time. 

While temporary broody hen cages can be built I find it best to have one permanently set up as this minimises the effort required to deal with a broody hen.

Other uses for a broody hen cage
A broody hen cage also makes a good holding pen for chickens that you are going to kill .  If I have a chicken I want to dispatch then I simply take it off the roost at night and place it in the broody hen cage for processing in the morning.  As chickens have virtually not night vision taking a chicken off the roost at night is much easier than trying to catch it in the chicken run during the day.

managing broody hens
For more information on broody hen management see: Managing Broody Hens.