When I got my hardware cloth, they had a big selection with different sizes. Get the kind with 1/2" squares. Coated is preferable (usually PVC coated, and I think it's usually green), but I didn't have that choice. I've had galvanized on my cage since September, and it's holding up just fine and doesn't smell.
I attached it with wire, because zip ties are plastic and easily chewed off. I'm not sure where to get the wire because we already had it here, but it's thin, easily twisted, and came in a roll, kinda like tape. I also used twist ties in some places, which work just as well. If you do use zip ties you'll have to check them frequently to make sure the rats haven't chewed them off.