I have thought about doing that, but never really done it, other than giving them excess veggies from the garden. I grew triticale & oats as a cover crop in an area about 20x50 last winter, ended up letting the pigs eat it, but it also could have been harvested for the chickens. It was very easy to grow but the labor of harvesting & threshing it into grain would have taken time.
I'm planting sunflowers, quinoa, millet & soybeans for them this summer. Alfalfa is easy to grow, which I have done, also.
Oh, and I have been raising mealworms for a couple years. They are a great treat, especially for chicks, but I can't produce enough of them to be an actual feed source for as many chickens as I have. They go dormant when it's cold and don't reproduce in the winter months.
There is an organic farm nearby that grows all their own chicken feed.
Kim