Roasting and baking are almost identical dry heat cooking methods. The difference lies in the foods being cooked. Baking refers to foods that need dry heat to set their structure such as breads, cakes etc. Roasting refers to meat and vegetables that already have structure and are just being cooked using dry heat.
Roasting and baking are basically the same except that roasting is usually done using a rack to elevate the food being roasted. The baking method is sued to refer to items baked in the oven without a roasting rack.