Traits for Craftsmanship
System
System-wise, your character needs to have the Abilities (Art, Biotech, Computer, Craftsman, Firearms, Hypertech, etc.) involved in creating a particular wonder… preferably at three dots or more in each of them, as noted above.
In the same vein, he must have the proper Spheres – at the proper levels – before he can place a given Effect into his creation. If Dr. Hans von Roth wants to build a car with Correspondence 3 and Time 3 Effects worked into its design, then he must first know how to work on cars and must have both Correspondence 3 and Time 3.
Obviously, a mage also needs an Arete Trait no lower than the Arete he wishes to build into the Wonder. If you don’t possess that level of Enlightenment, then you certainly can’t invest it into something else!
The Mage 20 section about Inventing, Modifying, and Improving Technology (pp. 463-464) has plenty of systems and suggestions for players who want to have their characters build or modify Wonders. And although those systems deal mostly with mechanical tinkering, those same rules apply to acts of artistry (painting, sculpture, song, etc.) and non-mechanical craftsman ship (woodworking, tailoring, leatherwork, and the like).