I found this work around that works for me on my Galaxy s4 active running version 5.0.1. You don't have to jailbreak or root.
First....i stored my downloaded music to my SD card. (make sure you have actually downloaded the songs to your phone....you have to press the pushpin icon and wait for it to download to your phone) You can do this by going to Play app...settings...storage location and choosing "external". It took a min or 2 but my music was moved over to my SD card.
After that....I went to the icon "My Files". Click on SD.....Android....data.... then com.google.android.music folder......files....music
All my music files were numbered. I knew the main songs that I wanted to set as ringtones were the last that I purchased. So I went to the bottom. Click on it to preview the file to see what song it is. (if you press and hold you can choose to rename the file to the song name if you want) press and hold and then choose Copy.
After this....the options are SD or Device. I chose Device.....Ringtones....then hit the "paste here" that's at the top.
After that, the song appears in your ringtones. if you renamed it, it will appear under the song name.