This is an advanced craft project that will require your parents' help.

Materials:
Mirror (a plain or beveled edge mirror will work best; any size is fine)
Plywood
Mirror mastic
Jigsaw or bandsaw (which your parent or guardian will use to cut the plywood)
Sandpaper
Pencil or chalk for tracing
Sizing (a special kind of glue used for leafing, which you can buy at a local craft store)
Silver/copper/gold leafing (you can purchase this at a local craft store: you buy a small book of leafing pages)
Foam rollerbrush for applying the sizing
Soft-bristled brush or paint brush

Step by Step

Step 1:
First you need to discuss with your parents where you want to hang your mirror. Using your pencil or chalk, trace the outline of the mirror on the piece of plywood.

Step 2:
Next, draw the shape that you want to frame the mirror (for example, lips or a flower — or any simple shape).

Step 3:
Have one of your parents cut the shape out. A jigsaw would work best, but they could probably use a bandsaw or a handsaw. At this point, you and your parent will have to decide how to mount the mirror, depending on the shape you are working with. If it's a smaller mirror, it's possible you could glue it to the surface with mirror mastic; if it's larger, you will probably want to create a small lip, or ledge, for the mirror to rest on. The opening in the plywood should be smaller than the mirror so that the edges of the mirror rest on plywood (this will make a lip to hold the mirror on the backside).

Step 4:
The plywood needs to be pretty smooth, so sand out any rough spots with a little sandpaper.

Step 5:
Using your rollerbrush put the sizing on the plywood cutout as evenly and thinly as possible. Let the sizing dry for about 10-15 minutes, until it is translucent and sticky when you rap your knuckles on it.

Step 6:
Then get your leafing ready. Try not to touch the leafing with your bare hands. This is why the little book with the leafing in it has tissue paper separating each page. Begin placing the silver leafing on the plywood one sheet at a time, using the tissue paper instead of your fingers to touch it.

Step 7:
Brush away the excess silver leafing once the surface is covered. You'll see how easily the excess brushes away.

Step 8:
Hang and enjoy!