This Instructable was inspired by the user Andrew Cleveland's beehive shelf. Here is the link:

https://www.instructables.com/id/Beehive-shelves/

This is a quick and easy project, great for beginners. Remember to always wear safety glasses when using power tools.
Be careful, be safe and have fun.

Step 1: Materials

For this project I used:
3/4 inch oak hardwood ply board (about 4 1/2 inches wide)
Wood glue
Two pipe clamps
Two spring clamps
A pencil
A rafter square
A carpenter's square
A ruler
Tape (preferably painter's tape)
Sand paper (I used 400 grit)
A hobby knife
A circular saw that will cut at a 30 degree angle
A pair of safety glasses
An extra pair of hands is very helpful

Step 2: Measurements

Use the pipe clamps to clamp the board to whatever you are working on top of. I used our picnic table. The outside measurement of side length on my shelf is 5 1/4 inches and my shelf measures 9 1/4 sitting on one of its sides.
If you want your shelf to be bigger make the sides longer.

Step 3: Start Cutting

Now that you have decided your side length, use the rafter square to draw a square at the end of the board, set your circular saw to 30 degrees and cut along the square line.

See picture for example of how to mark the lines.

Step 4: Cut the Pieces

First measure the length of your side piece and put a small mark there. Use the rafter square to make sure that the line is perpendicular to the side of the board.
Now sit your saw on the board like your are going to cut it (here is where you really want another set of hands). Now line the blade of the saw up with the line.
For this you need to turn the saw blade so that a tooth is right up next to the line (this is the most accurate way I have found to line everything up right).
With the saw still there slide the rafter square up next to the saw (the saw will most likely need to be turned a little bit). After this is done hold the rafter square firmly against the board, remove the saw making sure not to move the square and grab a spring clamp and clamp it down.
If your saw has a leader pointer it will be a bit easer.
Now cut the piece making sure that the saw is butted up against the rafter square and that the saw sits all the way down on the board while cutting.
You will need to flip the board over after every cut

Step 5: Ready to Assembly

Cut six side pieces.
Basically if you look at the pieces for the side and it looks like a rhombus for this angle you cut it wrong.

Step 6: Glue

Tape all the joints together except one and apply glue.
Wood glue works well.

Step 7: Assembly

Now that the glue has been applied, assemble the shelf and tape the last joint together.
Sit it on a flat surface to make sure that all the pieces line up. See picture.
Wrap one long piece of tape around the project. Now wait for the glue to dry.

Step 8: Clean Up the Glue

Use the hobby knife and sand paper to clean up any excess glue.
And you're done.

Step 9: Tips

Use wood glue.
Have someone help you.
Sand joints.
Try not to use duct tape if you can avoid it.
Measure twice, cut once.

My shelves did not come out perfect but I am very happy with them.
If one side is longer than the others the shelf will not fit as well. The same thing if any of the angles are off.

Remember to be careful, be safe, always wear safety glasses, and have fun.