>Half of the atmosphere from a Ringworld is a stupendous amount of gas Yes. So you would need to build it multiple of 10km. Assuming the pressure falls of 75%

>Half of the atmosphere from a Ringworld is a stupendous amount of gas Yes. So you would need to build it multiple of 10km. Assuming the pressure falls of 75% for each 10km (which seems about right from a quick glance at some tables), if it was 100km high the loss would be 0.25^10 of what it would be at 10km. So 100km wall would be ~million times less loss than a 10km wall.