Everyone who has answered has already given some great information. I just received an adult pair not too long ago myself. The male is around 8', the female is between 11 and 12'. After speaking with Dave Barker (vpi.com), I can't stress enough that you *must* watch your feeding habits with them. Most people that have adults, especially adult females, make them obese. According to Dave, these snakes have extremely efficient metabolisms, so they don't need to eat all that often. When they were breeding olives, they only fed the females 10 to 12 rats per year. Based on that information, you can see how feeding them on a "normal" snake feeding schedule (once a week or even more so for some people), would quickly make a fat snake. Evidently, fat females lay slugs or don't lay at all, which could explain why so few babies are produced. Currently my female is on a diet in hopes to have her ready late this season or early next season. I've introduced the male to her a couple of times and every time, he's interested. Now all I need to do is get her into the correct physical state and wanting to breed. If I'm successful, just keep an eye on the classifieds.
As far as enclosures go, I'd give a very young baby something pretty opaque so as to decrease the amount of stress as much as possible, then increase the size of the enclosure with the increasing size of the snake. Olives, when hatched, are somewhere around 20 to 21" in length, but rather slender. Housing should be pretty easy to figure out. Healthy adults, though long, are not nearly as massive as, say, burms of the same length, and require less floor space accordingly. However, bigger is always better, so go with as big as you can afford. Humidity shouldn't get too high as these are slightly arid climate snakes, and a water bowl should be provided at all times. I've noticed that at least my female drinks quite a bit. Anyway, best of luck with whatever you go with. Olives are awesome snakes, and I personally feel incredibly fortunate for being able to finally have the chance to work with them. If you'd like to take a look at some photos of mine, my gallery can be located here: http://gallery.pethobbyist.com/index.php .
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Chance Duncan
http://www.rivervalleysnakes.com