Where do you get it?
I might be interested in looking at this product myself, but all I can get locally is T-111 siding.
I have built some small mock up panels using regular ply with batten strips, wash / painted and glazed.
I haven't been able to find anything on plygroove anywhere except New Zealand and Australia, however I remember seeing some show about it either on HGTV of This Old House. i have found what appears to be the same thing, except that is appears to be some type of composite: http://www.fauxwoodbeams.com/ceilplanks-raised-grain.php
It seems that it would save labor over installing individual tongue and groove planks.
You could take 1/2 plywood (might get away with 3/8s), sanded one side, and rout the grooves in with the a triangular bit. You would build a simple router jig to be able to do this easily and have control when doing that many grooves. I would assume you would install these with the groove parallel to the ridge beam and use rafters to hide the end plywood joints. Just do the math carefully as the groove distance should be the same counting each edge of the plywood sheet as a groove. (This would need to have a bevel to it too but you could easily sand this.) The thickness of the plywood would depend on what your internal rafter support difference is. (16 inch, 24 inch, etc.) Construction adhessive and finish nailing would probably give the best result against sagging. There may also be a tongue and groove edged plywood sheet out there to start with.
If you did the exposed, support rafters every 4 feet you could cut the 4 x 8s down to 4 x 4 for ease of handling assuming the internal rafters were on 24 inch centers. I would even put the finish on before installing.
We did this years ago on a commercial building when we wanted an outside wall to look like 8 x 8 block but wanted to save money. The difference is we started with grooved siding and put in cross grooves. It has been up for over 20 years and still looks like block.