This here's the monocle I made for my steampunk costume. Its mostly made from sheet brass and copper, partly lined with felt for comfort. The bulk of the eyepiece itself is an old camera lens. The rivets are just flat-head brass nails.
There's a yellow LED behind the lens, which is run by the battery on the leather strap. Had to make a battery pack for the specific type of battery, which had to include a resistor so the LED wouldn't burn out. feh.
There's one smaller strap with a tiny buckle that runs over the top of the head to connect to the strap at the back of the head. I've found this keeps a lot of the weight of the monocle off my cheek.