Afraid I do not have a rare collection of DFM Data base but I do have a book that list DFC, AFC, DFM and it shows the date his DFM was gazetted with the words no citation.
I do have a copy of Air10 which says that he joined on 30/10/15, that he was storeman in the RFC and a Clerk in the RAF.
There is a AIR 76 for a W Roper at
The National Archives | DocumentsOnline | Search Results
which would cost £3.50 from the TNA.
Also in class WO339 there are the following W Roper's listed for files
WO339/70520, WO339/103263,WO339/116363 one of which might be your man.
There is a Lt W E Roper in class WO374/59041
Cheers
John-G
66 Squadron