Couple of bits of information.
First is a short piece from 'The Builder' dated Jun 29th 1889, describing the materials and decor of the house.
The next two are from the same periodical and show i) The elevations of the house (plus plan, as well as the gates - (still there, I think)) and ii) the plan and elevations of the stables, as well as the lodge house (also still there facing the A41?).
Finally, there is an aerial view from the 70's - the rose gardens mentioned in the previous posts can easily be seen as the nearly square dark outline on the right middle of the photo.
Hope they're all of interest.
Description: Builder 29th Jun 1889
Description: Plymyard House Elevations
Description: Plymyard House Outbuildings
Description: Plymyard Aerial 1970s