I’m going to reference my go-to post here (A Roon on (Synology) NAS Primer) and mention that, on the filesystem where you keep your music, you can create an m3u playlist that Roon will import as a “Shared” playlist during any scan of your library. You can create and edit these in any text editor, and all you have to do is get the paths right.
Let’s say you add a “playlists” folder at the top level of your music library folder. In there, you might have a file called “MyMusic.m3u” and its contents would look like the below (in Unix parlance, “../” means “up a directory, then follow from there”) - so, my “Non-Classical” and “Classical” folders are at the same level as my “playlists” folder, wherein I keep my .m3u files.
#EXTM3U
../Non-Classical/Lost Brothers, The/Halfway Towards A Healing/03 - Come Tomorrow.flac
../Non-Classical/Men At Work/Cargo (Remastered)/07 - High Wire.flac
../Non-Classical/Electric Light Orchestra/A New World Record/01 - Tightrope.flac
../Non-Classical/Tennessee Ernie Ford/Tennessee Ernie Ford_ Portrait Of An American Singer [Disc 1]/1-16 Slow Down.aif
../Non-Classical/Paul McCartney/Press To Play/06 - Press.aiff
../Non-Classical/Journey/Departure/04 - People And Places.flac
../Non-Classical/Various Artists/Stax '68; A Memphis Story/Disc 4/04 - Johnnie Taylor - Who's Making Love.aiff
../Non-Classical/Journey/Frontiers/04 - After The Fall.flac
../Non-Classical/Orielles, The/Silver Dollar Moment/07 - I Only Bought It For The Bottle.flac
../Non-Classical/Led Zeppelin/Presence/Disc 2/03 Led Zeppelin - 10 Ribs & All-Carrot Pod Pod (Pod) [Reference Mix].aif