Once the preliminary research is done, a 3-dimensional prototype can be created.   The most ideal material for this prototype is oil-based clay because it remains pliable indefinitely.  The prototype will be an exact replica of the finished sculpture, but on a smaller scale.  From the prototype, all the dimensions for the finished sculpture can be calculated, like a 3-D blueprint.

  Even in snow.... the yellow arrow points to the clay prototype used as a model.