Sounds like a good idea to get Roda to do this part. However, I do not think the package includes fitting because they could argue that they would not know exactly where you wanted the items positioned.
Are you sure the tiles are real marble? There are some excellent porcelain copies and some ceramics are now called rectified marble. This is a good question to Roda because if the bathrooms are real marble then the tiles can stain and be prone to minute cracks in the polish. I will add this question to my list for Roda! I work with the tile industry in design and know lots of tile fitters. Providing the tradesperson knows what they are doing I do not think drilling into the tiles/marble will be a problem.
The shower screen though is another bone of contention. I really think they should have finished off the showers properly. If the unit gets a leak there is bound to be an arguement that the shower screen was not fitted properly. If we can get Roda to fit these items (even if it is begrudgingly at extra cost) then I think this is a good idea and perhaps we should work on them to provide this service.