Add sausage (reserving 1/2 cup for gravy), cheddar cheese, and green chilies to the crockpot, stir.
Arrange biscuits on top, cover, and cook on high for 1 1/2 - 2 hours or low for 3 - 4 hours.
In the sausage pan, melt 4 tbsp butter on medium heat. Whisk in 1/4 cup flour, scraping bottom. Cook until light brown, whisking constantly for 1-2 minutes.