I think they can be.. But its hard to do something like that. My Chams are normally housed in cages 24X24X48 OR 16.5X16.5X48 which I think is big enough for a single chameleon.
I recently got a BIG cage 29X29X72 (260 gallon) I think its mega big, too big for a single chameleon, but thats a personal choice.
Cage size is honestly your choice. As big/small as you want.