Question

How did the glassmakers design their rose windows for the cathedrals?

Answer 1

The Rose print or Rose window was an architecturall element form the gothic era; very common in catholic constructions and later was also use in anglical architecture. 

The glassmakers had to make each piece of the window independently, following a basic design accordingly the symbology they wanted to represent.

Most of the times, the pieces of the windows were fit in a solid structure, that was added once the Church faccade was finished facade.