This insures proper drainage. Raised beds allow one to improve the gumbo soil with which Houston is plagued and provide proper drainage. Try to plant containerized roses as soon as possible after getting them home. The sooner they are in the ground, the sooner they can survive occasional lapses in watering. How far apart to plant your roses depends on the variety.
Hybrid teas take more space than floribundas.
Old garden roses can grow to massive proportions. Rose books will offer a guide to the eventual size of your rose variety. As a general rule plant floribundas at least 24 inches apart and hybrid teas at least 30 inches apart. These are bare minimums. More space is better.