This shelf is made out of free paint sticks and wood glue (elmers). Actually, I used about 10" of 1x2 pine instead of laminating 3 paintsticks together, but who is counting. To finish this shelf I used a bit of wood stain and poly-urethane I keep in stock, but if you do woodworking, that is always lying about, but I suppose I should say I used about $0.15 of stain and $0.32 of polyurathane.

Step 1: The BOM, the Tools, and the First Glue Up.

Material: 7 5-gallon paintsticks from home supply store. they are free

some white glue. I use titlebond, but elmers would of worked too.

some stain - I used golden oak

some poly-urathane - I used a water based semi-gloss,

Tools used; Band saw, clamps (lots), bricks, belt sander, sanding paper,

So the first thing that I glued was the back piece and the 4 verticals. the two end ones went up only and with the thickness of the back piece the 4 risers fit over the mirror.. For the two Middle risers that go down, I had to knotch out the piece to fit over the tiling. The down risers are important as they give most of the stability so the shelf stays level as the risers push back on the shelf's tendency to try and lean due to the leverage force against the attachments on the wall.

Step 2: Now Is the Time to Test Fit and Sand.

I can't stress this enough. The devil is in the details. Sand, sand, and more sanding. Round the edges, curve the corners, Sand the top down perfectly. This is by far the most time consuming part of the whole 2 hours it took to make this project. The sanding (and finishing) are what changes this from something in tom sawyers treehouse to a piece of furniture for a fine home. I used the bricks here to then glue the back support to the shelf AFTER all was sanded.

Step 3: Trim and Diagonal Supports

When I ripped the one painstick to make the back piece, I had a 1/4" piece left over. I sanded that down and added an edge to the shelf. I needed another painstick to make more of this 1/4" edge for the side pieces and the diagonals. These edge pieces are turnd 90 degrees, so the grain runs differently than the shelf piece. By gluing this on the edge (on 3 sides,) the edging will prevent the shelf from warping as the edging will have different grain lines than the shelf so each piece of wood prevents the other from warping.
Once the edging was dry, I glued the support piece to it. Once that was dry, I just took pieces of the 1/4" stock I made and wedged one side into the shelf-edge corner and held the other side against the outside riser and used a pencil to mark on the stock exactly how to cut the diagonal so it would lean properly agins the riser. Glue into place.

Step 4: Finishing Touches and Mounting.

I apply the stain with some leftover sponge packing material I got with something that that was delivered by amazon. Be careful to wipe drips with the stain really fast or you'll have a drip blemish on the wood. I also put 3 coats of the acrylic poly-urathane on the wood to seal it but still leave the wood with a satin finish that I wanted. If you want it more shiny or glass-like finish, keep adding more and more coats of the poly-u
To mount I got 2 sheek rock screws which are basically like deck screws on with even a more steep spiral for the thread. They pinned the back brace nicely against the wall and the risers in the middle keep the shelf from tilting with weight on the shelf. I wouldn't put more than 10lbs on the shelf either way.