Question
We live in central Pa.  On one side of our yard, there is a cement slab that I would like to cover with a raised bed, probably made of timbers.  It gets plenty of sun, most of the day.  I am interested in putting a rose garden there but because of it sitting on concrete I don't know how high to build it so there would be enough soil.

Answer
Most roses have roots that will grow from about 18 inches to 24 inches long. Ideally a container should be 36 inches deep. This depth means you can grow the hybrid teas which will have the most aggressive root systems. Because roses like their roots to be cool, giving them another foot in depth means they will have cool roots.