Most wire meshes are galvanized which means it is coated with zinc. this keeps it from rusting. Unfortunately zinc is very toxic to birds, this is why newer cages are coated with a zinc-free paint.
Most places will sell stainless steel mesh wires as well, this is a good choice but just to pricey for most.
polypropylene meshes work really well, there are usually a lot more options to choose from. Examples:
http://i00.i.aliimg.com/wsphoto/v0/31358...
http://www.parrotchronicles.com/features...
Edit: You didn't say what species of parrot you have, there beak strength vary greatly.
from budgie to parrot. it will be big aviary surrounding whole wall of one side of the room .so will parrot cut the mesh like butter (though unlike cage bar wire mesh can't be cut in half cz they will always hang to each other .my choice of size is 3/4 inch .though half inch is available but thickness of the wire is less than the 3/4 size also i feel it might too small to view birds properly .though little bit worried about small budgie head on the 3/4 size .maybe i will put all adult bird .so what you think .did you see any one with this type of setup .
