Determine which corner of the room the shelves will be hung, and decide on the size of the triangle shelves. They can be all the same size or varying sizes; one design idea is to go from small triangles at the top and progressively work down to large triangles.
Cut plywood board into the sizes you prefer, making as many shelves as necessary. Cutting the triangles into the correct dimensions will be easiest if the plywood is cut into squares first, then the sides can be run through a circular saw to create a triangle.
Put a keyhole router bit into a hand drill or drill press, and drill two ¼-inch deep keyholes into each side of the plywood board that will meet the wall.
Put a level against the wall and draw straight lines to map where the shelves will be hung. Place the triangle shelf against the wall and draw X’s that align with the keyholes on the plywood.
Drill a ¼-inch wide hole at the marks and insert the anchor. Put the screw into the anchor, leaving enough of the screw out of the wall so that the keyholes in the shelf have room to mount the screw head.
Line up the keyholes with the screws and mount the triangle shelves on the head of the screws.