it is generally not recomended to do grades in such small room. but if you have to have it, go ahead. i oculdn't have lived with flat layout. from my limited experience grades are about gradually increasing and decreasing and on your picture they do seem a bit abrupt. i wouldn't go for kit. fine tune your slopes with various temporary risers - toothpicks, match sticks, dowels etc.
roadbed is going to help the smoothness, i really like mine. but make sure your slopes work first.