I would look into researching bird parks such as the Kuala Lumpur Bird Park which has peacocks as well as many other birds. You could design a giant free-flight aviary or multiple themed free-flight aviaries.
Most zoos don't have enclosures for peafowl and just have them free-roaming. Many free-roaming populations of peacocks at zoos have been there for a very long time, so I guess zoos typically free-range them because it is just the way it has always been and the peafowl really aren't an animal they are focusing on displaying like they are the other animals.
The Bronx Zoo has an exhibit called "Jungle World" in which they used to display (I don't think they have them anymore?) green peafowl.
They were in the news a few years ago for having a green peahen escape the exhibit. Anyways, this is an indoor greenhouse type exhibit with a man made waterfall/river, underwater glass viewing, jungle plants, sculpted rock outcroppings, and a sandy bank. I'm pretty sure the peafowl shared the exhibit with other animals (possibly monkeys and tapirs) and of course the fish and turtles.
As far as vegetation it really varies. Clumping bamboo is nice and creates good shade and it is also native to some areas where peafowl are from. Lantanas are a nice flowering bush that are native to where Indian Peafowl are from and while the plant is known to be poisonous, my peafowl have always eaten the berries and leaves without being effected. It serves as a good bush for the peahens to nest under as well. Peafowl always benefit from having grass. They like to nibble on grass and overall it makes the enclosure look much nicer. An open area should be provided for the peacock near the guest viewing area where he can display his feathers for guests. It also wouldn't hurt to have an elegant perching area for the peacock to fly to for preening. Perhaps a pergola with passion flower vine climbing up it or some sort of beautiful flowering vine. Another optional feature is a small dust bathing area where the peafowl will flap around in the dust to clean their feathers.
KL Bird Park
Bronx Zoo Jungle World