Hi,
Thanks for the interesting question. Because you can't deform geometry in RailClone without a spline, I think the best way to solve this is by using two splines, one for the undulation, and another for the actual ceiling path. The undulating spline should be longer than the final path so that we can randomise its position without it repeating.
You can then use nested generators. An L1S generator adds a single ceiling strip along the undulating spline. This is then nested inside an A2S array to create multiple strips. To randomise them, we wire a Random Number node to the Left Padding. Set the Generate On value to Y Row and then each strip is randomly offset.
In the attached file I've also added a clipping spline to clean up the start of the spline and added a Sequence to allow you to control the number of strips.
I hope that helps, please take a look at the file and feel free to let me know if you have any questions.
All the best,
Paul