Nothing particularly special for these waxbills. They do like space, but then, what doesn't?
Cordon-bleus are much more willing to nest when kept in aviaries or flights
I've had less success in small cages, but I don't like small cages anyway
My pairs are in a variety of cages and flights. All cages are more flight cages eg below
Temperature - no lower than 15°C (60°F), especially important when breeding
Light for at least 12 hours a day (mine is 14)
Full spectrum fluorescent tubes are best, (but have to be replaced annually)
Link to Arcadia for explanation of the benefits of their Bird Lamps/ tubes
These tubes show all 'Blue' Waxbills to perfection.
Ideally, electronic ballast flicker-free battens (~ 20,000cps).