Step 1: Draw and cut out parts
Lightweight foam (usually from some sort of packaging)
A 60 degree set square or protractor
Something to use as ballast. I used prestik but you could use anything. taping a small coin to the nose will work fine.
2 beads or wheels
Now, From that sheet of thin packaging foam, cut the main parts out. Before you can do this, you should draw them first for accuracy and scale.
Start with the rotors - Basically 3 long rectangles, it is very important that each one is exactly the same or the rotorhead will be unbalanced.
Next will be the fuselage and rotor pylon. Draw to the scale shown with the fuselage about the same length as 1 rotor blade.
Then cut out the tail and the slot it should fit in. Also cut out 2 small circles and an equilateral triangle with each side the same length as the width of a rotor blade. Put a little bit of tape on either side of the 2 circles to reduce friction.
Bend the ends of the tailplane up as shown in pic 5.
Step 2: The rotors and rotorhead
Bend each blade slightly along the dotted lines shown in the second picture.
Also poke holes through the 2 circles and make sure all these parts can rotate freely around the pin.
Tape the rotor pylon to the top of the fuselage as shown.
Put 2 beads onto the pin, then one of the 2 circles. Then the rotor base (triangle), other circle and 2 more beads follow.