Baking is a process available in some 3D programs such as Cinema 4D and the free Blender. Although this process is not essential, it can greatly improve the appearance and effectiveness of your multipliers.
Baking uses algorithms to compute accurate shading for your mesh based on lighting and it will generate a texture ready for converting to a professional-looking base for a multiplier. You can then touch up this base with small details as needed, resulting in a truly professional looking multiplier. The image below shows a baked multiplier for a window.
If your 3D program does not support baking, it doesn’t matter. You can usually export your meshes as an OBJ file (a universally adopted format among most 3D applications), which you can then import into an application that does offer it.
For more information about the merits of baking and drawing multipliers by hand (and for information about creating a good multiplier either way), see: Object Creation Part 2: Object Textures.