If you think dwarf jacks only get about 2 inches, its time for you to keep studying on the chameleon species.
As I said before, don't fit a chameleon to a cage, fit a cage to a chameleon. Pick the species you are going to keep as your first, I reccomend a veiled chameleon, possibly a panther chameleon, read the care requirements. Study how other people keep them. Make a cage, test it out for a week or two studying the temperatures and humidity, airflow, etc. Post photos of the enclosure online to have Experienced people give you their opinions on what the cage should have to better suit its future resident.
THEN... then if everything is adequate, make your purchase through a reputable company or breeder of a completely healthy specimen.
No doubt you will have to make minor adjustments tot eh cage during the first month, but its likely those will depend on room temperatures, seasonal changes, or the areas climate in which you live in.
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CANADIAN SILKWORMS