Ok, so I'm assuming you have your wiiu/apps/retroarch directory since you have retroarch available to even launch, right? And a /retroarch directory on the root of your SD card? Try my /retroarch directory to get you started. I did delete the cores I won't personally be using, so you'll have to add those back from the official download if you want them. You'll also have my issue with the ozone driver that playlists are blank when you select them, but you can always just not use playlists or switch back to the xmb driver.
Note to mods: there are no roms in here. It's just the /retroarch directory from the official download with the assets downloaded from my personal SD card for him to try.
Hopefully this is the right link, I've never actually uploaded to mega before, just downloaded.
https://mega.nz/#!abozgCza!xY1A4TomH6L53IwNtzNvosWNCBOJBc6ZMADKhIyj-Js