Hi Michael,
Thanks for contacting us and the file. In this case the distortion is caused because the surface and the clipping spline are close to one another. As you've mentioned the only way to solve this is to enlarge the surface so that it extends beyond the clipping spline. I've amended your sample scene to show how this could be done.

The surfaces being used by RC are hidden, but can be found in the
Surfaces layer. I created them by splitting the edges for each face of the roof and using
Racoon Artworks Extend Borders script..
To add end caps you should be able to add additional geometry to the
Left and
Right inputs of the Generator. Also changing the generator's
Default mode to
Adaptive will prevent sliced edges unless the roof is cut at an angle. To slice from the top instead of the bottom you can rotate the array by 180 degrees using the generators
Properties > Clipping Area > Z Rotation value, just remember to adjust the padding and rotation for the tiles too.
At this moment the best way to solve roofs - unless they're very simple - is with one RC object per side. I appreciate that this can be complicated but we do have plans to introduce new tools to simplify this process. In the meantime you may find the script attached to this post useful. It allows you to select a RailClone object and apply it automatically to selected polygons. Here's a quick demo:
The script works by automatically extracting a closed spline from each polygon. It then duplicates the selected RC object, orientates it so that it is aligned with the polygon's surface normal and finally assigns the spline to the RailClone object's Clipping path. In most cases you should find this means you don't need a surface if the spline is flat, if not as in some of the sides of the roof in your example, you may still need to add a surface to get the correct shape.
To use it:
- The surface must be an Editable Poly object with no modifiers applied.
- The RailClone objects should have a clipping spline applied with the Generator set to Get X/Y Size from Area. The Clipping spline needs to be the first entry in the Base Objects rollout. If necessary you can use the arrows change the order.

- Run the Script and use the Pick Rc Object button to select the RailClone object you'd like to clone.
- Select the polygons on the surface and click apply RC to Faces. The script will create a new clipping spline and RailClone object for each polygon
- Alternatively hold shift and click RC to Faces and the script creates a single spline and RC object that combines the selected faces. This is most useful when all the faces selected are planar.
I hope that helps, please let me know if you have any further questions.
Many thanks!
Paul