Black headed monitor

[Emma96]

Hey guys would a 3ft L X 4ft H x 2ft W be okay for a Black headed monitor or would I be better off going smaller?

 

[Imported_tuatara]

no. not for either subspecies, they're much more terrestrial than arboreal, 4ft L is the shortest for the smaller subspecies, 5-6ft L (imo) for the bigger.

 

[Bushfire]

I think you'll be fine with one in that size. My advice for that would also be make use of side walls and if possible roof.