At this time, there is no way to import your own materials/textures. You can customize the textures provided by changing their scale and angle of the material pattern.
To customize existing materials:
- Select Materials from the main Design Menu across the top.
- From the left menu, choose the category and material group.
- Select the material that you want to apply.
- Apply the material to a surface. While that surface is selected, look to the options on the right for Scale and Angle settings.
- Change the values to rotate to pattern or change the size of the pattern by a scaling percentage from the original pattern.