This instructable will more or less show you an inexpensive way to make a unique mirror frame for an octagon mirror. This is my first detailed instructable so it is not quite

What supplies I had laying around, and what you will need (what I used):

Octagon mirror (hobby lobby, $3 on sale)
particle board ($6 for a big rectangle of it)
1 x 4 board (I bought one 8 foot board) ($3)
Spray Paint (walmart, $4)
wood glue ($3)
brad nails ($? came with nail gun stash)
sandpaper ($3, but I had some laying around)
staples ($?, staple gun type, had them)
mighty putty (as seen on TV, $10, I've had some laying around for years)
keyhole mount/hook ($3)

Total estimated cost: $32-$50.
I happened to only have to buy the mirror and the spray paint, I had everything else laying around from my LED wall lamp I made.

What tools you will need:
brad nail gun (mine was air powered with an air supply)
staple gun (hand power)
miter saw
Jigsaw

Obviously if you don't have the tools the initial cost of the project skyrockets :)

Please be careful with the miter saw! Use proper safety tools and follow all warnings you come across! Don't cut off your fingers with the miter saw, it will ruin your day and your nickname (no one wants to be called "Stumpy" or an ironic "Fingers McGee" or something).

Step 1: Cut Out Back

Place your mirror on the board, and trace around it with a pencil. Use a jigsaw to cut it out.

Step 2: Measurements and Angles

Measure the mirror. For an octagon, this mirror had 5 inch sides. Most miter saws have preset settings. The angles for an octagon are 22.5 degrees. My miter saw had that as one of the presets. It ended up being 5 and 1/4 inches per piece of wood.

Each 1x4 became a 1x 1.5 after cutting them up. BE SUPER CAREFUL HERE! Make sure you are aware of how a miter saw cuts, and where to put your fingers, because the wood is too small to use a clamp here (unless you know a way) If you cut it wrong, keep the cut or just get a new 5" piece real quick and try again.

I only used 4' of an 8' board, so I had plenty extra for mistakes. You will see I cut 3 of the sides too short. I didn't particularly care, I just flushed up the front, and the back isn't really noticeable on the wall anyways.

Step 3: Assembly

After this I matched up my pieces, and nailed one at a time to the frame. My frame was super close to symmetrical, but not quite, so depending on how well I turned my corners with the jigsaw, my corners weren't all 5 inches on the dot, so I numbered the pieces and shaved off what was necessary with the miter saw to make all the pieces fit right. Then I nailed them, making sure the front was all flush with the next. They were 1 inch nails.

After nailing the pieces straight in to the frame, I put brad nails into each corner too for secure the pieces to each other as well as the frame.

Step 4: Sanding and Glue

Sand the 1x4 pieces, it will take the paint a little better. I used the wood glue to fill in any small gaps I had on the edges to it has a more flush appearance after it's painted. Let it dry good though.

Step 5: Paint the Front, Then the Back

Follow the spray paint instructions! This paint needed three coats to cover the wood adequately. It says to not try to cover it all in one try, and 3 coats did it for me. This part made me wait! After 3 coats (waiting 15 minutes each) I had to wait a few hours for it to dry.

After the front was dry, I taped off the back (I didn't want the back to look too ghetto). I used three coats again on the back edges. After that was done, I set the frame out in the desert sun for the afternoon.

As you can see in the picture, when I reused the same plastic for painting on the floor, the new paint stuck to the old paint on the plastic and pulled up when I picked up the frame again. No big deal, I used sandpaper to make it look normal again :)

The mirror almost didn't fit so when I attached it to the frame I had to repaint the inside edge. I just taped off the mirror really well and painted what needed painted again.

Step 6: Mirror and Mounting

I used mighty putty because it was handy. There are all kinds super glues and stuff at a hobby store or even walmart, I used the mighty putty epoxy. After mixing it I put it in the four corners and pressed the mirror firmly into place. I let it dry according to instructions.

I then took my staple gun and just in case the glue ever quit holding, I put one staple in each side with the staple gun. I made it a point to not put the staple in too far when shooting it in.

I had some felt strips I put around the three sides. I did this so the mirror would hang straight out and not be tilted in any way by the keyhole mount I used.

Note: you will have to find tiny screws that won't go through the board into the mirror, the screws that come with the mounting hardware are too long.

That's about it! Thanks for looking if you did, my wife likes it a lot anyways :)