Step 1: What you need
Saw (I suggest a circular table saw, for precise repeatable cuts)
cardboard for template.
some scrap wood.
baking paper (or anything else to separate wood while gluing).
belt sander (Use a fresh sanding belt!)
Sandpaper or sanding machine to sand concave forms
Step 2: Design phase
I had 2.3cm thick multiplex board, therefore I needed 16layers. each layer is made up of a frame of 4 pieces of multiplex strips (makes 60 strips + 1 baseplate).
I wanted a maximum wall thickness of about 2.5cm (as you remove quite a lot of material to round it, you should make the wall thickness about equal the board thickness).
So I had to cut strips of 2.5cm x 13.5cm. and a base plate of 16cm x 16cm.
As I wanted to have a half revelation each layer had to be rotated by about 11.2 degrees.
To easily measure this rotation while stacking up the layers I built a template of card board that had 2 crosses on it. The second cross is rotated by 11.2 degrees from the first one. I made short cuts in the end of the crosses. When i put the template on each frame and make marks on each frame i can easily align the marks and create a smooth revelation.