Yes you can cook a roast 2 days in advance and store it properly in the refrigerator for upto 4 days. You must remove the roast from the refrigerator about 2 hours before serving time and allow the roast to come to room temperature. Then reheat the roast in the oven or microwave. The time taken to reheat the roast would depend on the weight of the roast. Using a meat thermometer is the safest way to ensure that you do not over-heat or under-heat your roast. 

Here is a blog that helps you understand how to store a roast. 

how-to-store-a-roast-properly