As long as you can provide the correct temps and humdity, no cage can be too big. Now it can be too sparse in that you need to add stuff like silk vines, corrugated drain pipe, PVC pipe, hides etc. The key is to not leave a lot of open space for baby BPs in between the hides. Make them feel safe traveling between hides. Once they get big, it depends on the snake. Dottie personally cares less about open space now and sits out half the time lol. if you look at the 4th cage down on the left stack, that is Dottie's cage and you can see i just give her 2 hides and she is content with that and her shelf. And ignore the hide lol. It is too small for her but she loves them. I gave her bigger hides and she clearly wasn't happy.