The weight capacity of a custom shower curtain rod depends on the mounting technique and hardware used.
Most high-quality shower curtain rods are made from heavy-duty brass rather than stainless steel because brass has higher corrosion-resistance. These brass models can typically support between 20-25 lbs.
The more ceiling and wall supports you have, the greater the weight capacity. Ensure that you mount the shower curtain correctly in wall or ceiling studs instead of drywall using the anchors and screws provided to get the optimal load-bearing capacity as specified by the manufacturer.