These work great and are economical. Don't expect that the opening will stay round, the birds will chew it until they are satisfied with how it looks.

It is made of plywood, so there is glue in there that the birds chew, but I haven't had any health problems resulting from it.

The end is such that you can mount it inside the cage, or if you prefer, on the outside so that you can access the inside of the box with ease.

It is a pain to clean once the babies hatch, but if you use a lot of wood shaving bedding, it soaks up most of the poop and you can empty and replace it once a day for the duration of the time until the babies come out and learn to sit on the perch themselves and eventually eat. Make sure the wood shaving is not pine, as that is poisonous.

Pros: I've had success with these

Cons: The birds chew the opening a lit bigger

I sold lots of these, they are a must have for breeders. I have seen homemade ones but they are not nearly as nice. They are however hard to clean. Make sure you get the right size because the birds get crowed.

Pros: not work, already made

Cons: hard to clean