The below pictures and instructions
will provide a clue of how these Megaliths were built. This is of
course, the Type I Egg Plan. Remember that Professor
Thom found that he could use the Megalithical
Yard to construct these plans.

We begin with two pythagorean right angled triangles as shown above. The lengths of CA and BD are the same, and can be of any reasonable length as shown.

After, we use the length of OC or OD to be the radius of a circle, and we draw a semi-circle as shown.

After constructing the semi-circle, we construct two lines EF and EG. These two lines should be short in length, and can be drawn as reasonably shown above.

To finish with the above picture, we use BC and AD as radiuses to construct
the arcs CG and DF respectively. After, the arc GF is made by using
the lines EG and EF as its radius.