I made a short video and posted it on Viemo on my efforts on creating this: https://vimeo.com/49469767
Firstly I started with a generic Adaptive Component family template and created a simple extrusion between two (Adaptive) points. "Saved this as Adaptive Rafter".
Start a New Conceptual Mass, and using the Splines Through Points tool draw two lines that will represent the two sides of the outline of the undulating ceiling.
You can refine the location of the outline of the ceiling by creating a grid and accurately placing the pline node points according to your design, you can then manipulate the height of the nodes under the properties.
Using the Divide Path tool to specify how many components you want arrayed along the two plines which are the outline of my ceiling, attach the first point of the adaptive component to the first node on your spline and then the second point to the opposite node.
Use the Repeat tool to array the component along your spline placing components along the divide path points.
You can then flip to a 3D view to manipulate the node points flexing the design.
Couple things to remember when playing with the Repeater, check the properties when your creating it, there is a check box that will make the component "Always Vertical" when you load it into your new Mass.
If the path has adaptive points, check the Orientation parameter of those points in regards to placement; sometimes you need the points need to be "orthogonal", sometimes "vertical", etc.
Got this advice from Alfredo Medina when I posted a query on the Autodesk Forum.
Pretty cool stuff!