If they are under an inch in diameter, you can bake them whole. Personally, I love the look of roasting whole carrots. They just look so elegant! However, if they're too thick, you can slice them in half, lengthwise or cut them into 'coins'. I like slicing them on the diagonal when making 'coins' so they have an oval shape. Just be sure your slices are uniform in thickness so they cook evenly.