Chipotle Mexican Grill Inc., a Denver-based casual dining chain, warned that fourth-quarter earnings will miss estimates because of higher food costs. It also said its catering service will be available in Colorado starting Monday and will roll out to all of its markets in coming months. It has been selling ‘‘burritos by the box’’ for smaller catering orders. But the catering service is designed for 20 to 200 people, with each person able to customize meals, as they would at the restaurant.