I'm not sure I understand the question. Most gardeners dig down 1-1/2 to 2 feet for roses. If the bed is raised 4 inches above the soil line, you would still need to dig down at least 1-1/2 feet from the top of the soil--4 inches plus another 14 or more inches below it.

Hope I didn't miss the point of your question.

You will probably get more responses if you post your questions over on the main Rose Forum (the "discussions" part.) This section here is more for chit-chat on a wide range of topics.

Good luck,
Kate