I have three melleri in 2x2x4 cages. These melleri are not adults though.... One of them is close to adult size but needs to be kept in a smaller cage due to a condition. The other two aren't full grown and do just fine in the cages. I wouldn't say melleri are lazy... but some can be. If you had a melleri wandering the cage a lot and climbing the sides I would build something bigger for them to wander around in. The larger cham of the three that are in the cages doesn't have much of a wandering routine, and neither does one of the medium sized melleri. Both have a pretty simple bask/sleeping routine where they tend to be in either spot... or hunting crickets.. otherwise they bask, move to a cooler spot, bask, move to a cooler spot, and then find their sleeping branch. All three melleri sleep in the same exact spot every single night.
If I had to keep a melleri caged into adulthood I would buy two 2x2x4 cages and make a trip to Home Depot or Lowe's and buy some hardware to connect the two cages... Or build a cage in similar size.
Melleri need more horizontal space to stretch out on and to move around on. They don't really need much height. My large melleri, Henry (23" from nose to tale tip), lives in a free range that is 2' deep 4' wide and 3.5' tall. He moves around in it during the day depending on if he wants to bask or sit in the shade or sit near the window to look out.
Another cage option is the reptarium cages... using a 30x30x48 standing up or on it's side. The only big issue with these cages is the mesh the cage is made out of in regards to lighting. You'll need to use 10.0 zoomed UVB lamps and I would definitely use 6500K lamps to provide more visible light and growing light for the plants. These cages are also a bit harder to clean...
I would build a custom cage if keeping melleri in cages. you could build something as simple as PVC piping and plastic mesh from HD or Lowe's...