You will need two cages regardless, as any new animal, even bought from a reputable breeder, should be quarantined away from your own animals. Keep him in a separate cage in a separate room if possible, for at least a month. A fecal should be done to make sure he has no parasites. Three months would be much better quarentine period to ensure no diseases etc, aren't incubating. Three months with a fecal done once per month so you have three clean fecals over the three month period and a clean bill of health from a qualified vet, is the best way to go before introducing a new dragon to an existing healthy dragon or group of dragons.
Basic quarentine measures aside, a male and female housed together will have a very high chance of breeder and producing fertile clutches. A male constantly bugging a female to mate can cause her undue stress, prevent her from eating and feeding properly, get her pregnant which will only had more stress to her health. She will need extra care, extra feeding and attention to ensure she can carry frequent clutches, about once every 3-4 weeks on average. She will need extra calcium to ensure her calcium levels don't drop etc.
Even if no eggs are produced, having another dragon in the cage doesn't mean they will get along. One or both may seriously injure the other, including tearing off limbs if the fights get severe enough. An attack like this can happen in a flash, you could see them basking peacefully on their logs one minute, come back in another and see a dragon all covered in blood with a missing foot the next. It may never happen, but it can happen and it has to other people who have posted here.
Thus, my suggestion, get a second cage of the appropriate size and not bother trying to put them together. Also don't have them out together either, as it only takes a couple of seconds for a male to grab a female and mate her.
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PHLdyPayne