I don't think there's any problems with using a 3' tall cage. I have found that they (GTPs) do seem to prefer sideways thermoregulation as opposed to vertical so if you go with 3' tall, I'd make sure it was at least 3' wide too in order to provide the sideways movement.
The "roomy" standard for a GTP would be a 3x2x2 (WxLxH) but, unlike BPs, there's really no reason you can't go bigger.
Reply With Quote