What do you consider essential in a ROO's diet? Need backup

I've long searched for the best info about this. Hopefully this will help others as well. Thank you

I just need the simple version - if one goes to the feed store to buy food for their roo, what should they come home with? Thanks!

If someone (not I) is only feeding their roos layer food and a bit of scratch, what will happen?

Thanks Carla, Helena.
The roo I have in mind thrived for 5 years on sunflower seeds, wild game bird food, scratch, oats, fruits and veggies (e.g. grapes, blueberries, raspberries, blackberries, tomatoes, squash, watermelon, cantelope), Avia Charge 200 in water, and other things too, all things recommended over the years on BYC. Plus plenty of bugs and plants from free ranging. He is now in a situation where the people want to revert to just giving him what they give the hens - layena and scratch (as well as free range in the summer when the weather is good) . I have never seen him eat layena - rejects it - so he will be in trouble unless he is moved to partake because he has no other choice. It will all be a big change for him - and I don't know whether he will be okay or whether he needs to get out.

Thank you Diana - info very much appreciated.
When I called feed stores and MH to see what they would say about a roos diet, they hesitate and then say "layer food". This is the answer most places give and so it is hard to convince anyone that they should do otherwise, yet the all those studies would seem to indicate the roos will have health problems on a primarily layer food diet.
If anyone has any other great user friendly info (something I can get folks to read) about what roos should and shouldn't eat, I'd be grateful and happy to spread the word.