YOU WILL NOT GAIN MONEY BY BREEDING BUDGIES!
There are many things that need to be considered before a nest box is even put down on the shopping list.
Age: The age of the breeding birds must be known so that you know they are mentally and physically ready to rear offspring. The youngest that most breeders accept as a safe age is one year. Many feel that 18 months is better. Budgies themselves are physically able to breed by the age of 6 months, but in humans years this equates to 13 -14 years of age. At 6 months they simply are not mentally ready for the task of breeding.
Many problems can arise if you attempt to breed with budgies that are too young. They can start to eat eggs, which once started can be hard to stop a bird from continuing, they can abandon nests and eggs or worse attack the young when they hatch.
Birds from a breeder you should expect a correct month of birth if not the actual date of hatching. I’m not meaning off the top of they heads but they should have it some where in their records. Older birds in the show side should have coloured bands on their legs which will give you a year of hatching. Ones from pet shops can come with leg bands but if you clearly tell them why you want to know the correct age they should be able to tell what info the breeder gave when selling them. You still take these ages at a risk that they picked a figure from air to tell you for a sale.
If you have purchased your birds from a reputable breeder they should be able to give you an accurate age of the bird by checking their records. If the breeder also keeps exhibition budgies many will also have leg rings which will indicate the year of birth Ring on Budgie Leg
You also need to know if your birds are too old to breed. Hens should not be used over the age of three to four. Sometime a breeder will use a 4 year old hen, but will move the eggs to another clutch if the hen is of high value. This is to reduce the stress on their bodies that that experience in raising a clutch. Males shouldn’t be used over the age of 6.
Once you know if your birds are ready or not you can look at other issues.
Health: Both the hen and cock need to be in tip top health. You need to make sure there are none of the normal signs of illness: Sitting fluffed up continually, Discoloration/discharge present on feathers above nostrils, Lethargy, Vomiting, and Inability to balance, Stains or accumulated poop on vent feathers. If you can’t tell this apart rethink your idea of breeding them right now and study their behaviour. You can also take the birds to your vet to get a well bird check up. They also need to be in breeding condition. The hens will have dark brown cere or turning brown while the males cere will be a deep and even blue (or a deep pinky/purply cere for some breeds, such a fallows, inos and recessive pieds).
Relationship: The hen and cock should not be closely related. The closer the birds are in relationship the greater the risk of defects and problems arising. Beginner breeders should not consider line breeding (an advanced mode of breeding used by experienced exhibition breeders), as it takes a lot of effort to do correctly. The closest most people deem acceptable is grandparent to grandchild or aunt/uncle to nephew/niece. But Line breeding or inbreeding can not be taken lightly .
Set up: Yes, using a normal bird cage can work but you need to think about where to put the nestbox. If it is inside the cage, is there enough room for 2 adults and up to 6 - 8 chicksl? Make sure you have enough clear space around the sides or ground to either hang or place extra seed dishes and fresh food plates.
Hand feeding: You will need to have hand feeding formula before any babies appear for the in case moment of having to feed a newborn chick. Added to the food are syringes for problem feeders and a spoon bent into a spout. It would also help for you to visit a breeder or a vet that handles bird who can show you the way to feed them correctly.
Afterwards: What are you going to do with the chicks? Give them away to friends and family, sell them privately?, sell them to a pet shop or even keep them. What ever you choose to do it needs to be thought over first.