>>today i will be getting a new iggy. what is the ideal cage size for the ig around 6 inches st length?
Iguanas do most of their growing during spring and summer. Iguanas can grow 12 inches a year.
Is that 6 inches the body only (SVL) or the entire iguana, from snout to tail tip (STL)? If STL, then you could start off with a 50 gal minimum, but you are going to need to move him into an adult size enclosure (see my Basic Cage Design Problems article) by this time next year. If not sooner.
>>and when can he start free roaming?
After iguana-proofing the rooms you are going to let him out in, or your entire home, part of your taming process will be to let him out for supervised out-time, afater having set up basking and lounging areas for him. My iglets are all free-roaming by the time they are 7" SVL (~9-10 months of age).
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Melissk
anapsid.org
Iguanas for Dummies