1 ft will not be deep enough for roses. 2 ft would be more adequate. Roses do need good drainage. You should not put soil over your trees roots, it can kill it. You can post this question on the trees and shrubs forum to get more response/ideas on that question. Roses also do best in full sun and would probably do better without competing with the tree roots. Do you have an area away from the tree that is full sun? That would be best for the roses.
