That’s right !

The 2X15 episode of the SGU series allows me to answer to my question, namely : what are the angles of the sides of the gate ? Are they equal ? And what about the moving ring, is it equal too ?

The answer on the picture:

So it’s really easy to calculate this angle knowing the width of the central and outward ring.
The sequence of operations will consist in showing an approximate model from a piece of  the gate that will not have details, only a form on which thereafter we could sculpt all the rest.