Baby crested Geckos tend to do well in smaller enclosures as they can struggle to find their food in a larger environment. Medium plastic or glass faunariums of around 18x18x12cm can easily hold 1 or 2 young crested geckos up to around 5 or 6 months old, once at 6 months or around 15g a larger enclosure will be needed to ensure that the gecko gets the required exercise from climbing and exploring.
For a single adult or pair of juveniles a 30x30x45cm sized Tall exo-terra is OK, but Crested geckos will make use of any space given to them so bigger is always better. A pair of adult cresties can be housed in a 60x45x60. Be aware that male cresties should not be housed together as they are territorial and will fight with often fatal consequences. It is recommended if you want to house multiple adults together, a small harem of 1 male to 2 or 3 females is advised. Permanently housing a male with only 1 female can often cause stress to the female as she would constantly be being pursued by the male to mate. If you are housing male and female geckos together, you will need to provide a suitable lay-box for the female/s as without one the female can retain the eggs and become egg-bound which has major complications and can lead to death.