With a $12 plank of pine you could make four of these, I'll show you how I made one. Here is how to make a strong corner shelf that can bare the weight.
I took it over to my local Pittsburgh Techshop and made a couple within 2 hours.
Step 1: Plan Your Cut
First we make a cut plan on the board. This is rough because the saw is going to eat some wood each time it cuts and change our dimensions. So just draft it out and plan for the first cut. Use Pencil if possible.
Step 2: Table Saw
My first cut was to shorten the board so I could square it up and cut it down the center. I used the Table saw and Miter tool.
Step 3: Prep the Base.
Now I have two Triangular Pieces. (The second piece will be fore a floating shelf demonstration on a different instructable) And I used the table saw to cut two 2" pieces off of the original board. These will be for my mounting base.
Next I will cut the tips of the base pieces at a 45 degree angle to match the top board and clean up any additional board length.
Over to the drill press where I will screw in some 1/4" holes for wall mounting later.
Then bring the board back together and see if it all fits nicely together. Sand any rough edges and cut any longer than necessary segments.
Step 4: Almost Done
Now that the base is assembled just use some finishing nails to connect the top and sides. Use clamps as necessary to hold your project still.
It is done, but I'm going to take it one step further by sanding the top and adding wood stain it Kona (black, okay color).
A day and a wall mount later and now I have a corner shelf that will support a lot of weight. Give it a go and leave your comments below.