A little touchy to raise,but they do need to be raised on a wire floored pen.Should also provide lots of branches for them to hide in.
I have never raised grouse,but I'd assume gamebird feed and live insects.I'm sure there is someone on here that has some experience in raising them.
I agree with raising them on wire and providing branches so they can hide. I use the softer UV resistant deer netting for all my gamebirds' pens' ceilings I've found it lasts a long time, provides some shade, and keeps them from hurting themselves if they fly into it. Grouse love mealworms so those are a good treat as are fruits like blueberries, raspberries, and small blackberries. It's up to you how much you want to spoil them but this is what I do for my pheasants and game fowl