If Im cooking a roast in a slow cooker when do I add the vegtables?

Im new at using a slow cooker, and I must say so far I love it, today I have a small roast, and wanted to add potatoes and carrots, they are raw, so do I add them same time I start the meat? Or do I let it cook for a few hours then add the potatoes and carrots, the carrots are small baby, and the potatoes I quartered redskins?