When should a BP be moved to a larger tank?

[zina10]

I would upgrade when the space is getting to small to hold 2 hides, one in warm and one in cool end, as well as an appropriate sized water dish.

Many people keep them quite well in smaller enclosures and tubs, I like to keep them in display cages, so they have a lot of room. However, my enclosures are professional reptile cages, so they hold heat and humidity very well, and also keep the snake feeling safer because of solid sides, back and top (not see through) Also easy to maintain and keep clean.

I make sure to have lots of places to hide and to let them thermoregulate.
Large glass cages are IMHO a real pain to deal with. I would rather get a used reptile cage (and clean + sanitize very very well) then a new, bigger glass tank...