custom terrain material is not showing up

I am trying to create my own terrain materials in the material.cs file like this:

1. new TerrainMaterial()
2. {
3. internalName = "MYSnow";
4. diffuseMap = "levels/mmap/art/terrain/snow_terrain_base";
5. diffuseSize = "4095";
6. normalMap = "levels/mmap/art/terrain/snow_normal";
7. detailMap = "levels/mmap/art/terrain/snow_detail";
8. detailSize = "121";
9. detailStrength = "0.1";
10. detailDistance = "500";
11. macroMap = "levels/mmap/art/terrain/snow_macro";
12. macroSize = "3";
13. macroStrength = "0.45";
14. macroDistance = "120";
15. };

but when i go to the terrain painter to select it it's not there, there isn't much online about it so don't know what to do, any idea what i'm doing wrong?
thank you

 

so to create new terrain materials I only need to modify the materials.json in the terrains folder with the relatives textures, no other files are required?