Hey, what you should try to do is hang the nest box outside the cage, For ex i have 5 dors on my cage 2 up top two down below and one big one, i removed one of the door so there was just a hole and stuck the nesting box opening there, this way its accessible to the budgie when there inside the cage but the box does not take room inside the cage. My female got very nasty when i put in the box, she stayed in there and bit who ever tried to get her out of the box, and she only came out for food and water, Good luck