3ds Max has long been the pro-grade 3D authoring tool for GTA mapping. This is an overview of the tool, not a tutorial.

What it does in the workflow

Creates 3D geometry. Handles materials and UV mapping. Allows skinning for animated objects. Plugin export supports YDR/YDD formats for use with GTA.

Most professional MLO makers have 3ds Max as part of their pipeline.

Cost and licensing

Paid. Licence is expensive. Many indie creators use Blender instead (as it's free).

Should you decide to build your creator station from the ground up, the lightweight GTA 6 creator utilities (planners, generators, RP-economy calculators) are free and complement whatever 3D tool you choose.