My second step in buying a rose is to consider the disease resistance of the potential purchase. Many roses are susceptible to a variety of diseases and in my area (Piedmont of North Carolina) blackspot and mildew can be problems. They do not generally kill a rose bush but they can make it look unsightly even with a regular spraying program. I try to reduce this problem by picking disease resistant roses and there are many. Determining the disease resistance of a rose is probably the biggest problem; the Encyclopedia of Roses, put out by the American Rose Society, is a great resource for this information. Read tags on the rose as it often will include this information.
Next, you have to decide if you want to buy your rose bare root or in a container. Both can be purchased at stores and garden centers, or by mail order. In general, bare root roses from a reputable dealer is a better value. They are less expensive and completely satisfactory. Reputable dealers keep the roses in cold storage and will ship them to you during the appropriate time to plant them. The local stores that carry bare root plants do not keep them in cold storage and the roses will begin to grow while they sit in the store. These are not a good value. In addition the wax on them will cause wilt once the summer’s hot sun temperatures hit. That being said, I will admit that I have bought bare root roses from big box stores on an impulse and had enough success to do it again, but only if the roses are still dormant and not leafed out. There are many good mail order rose growers and dealers, Jackson and Perkins being the most famous. Their selection is limited if you want old garden roses or modern shrub roses, but they have a large selection of hybrid teas and floribundas.
The alternative to a bare root plant is one that has been planted in a container. These may be purchased almost any time of year both from retail stores and on line. They are generally more expensive than bare root plants but you may be able to see the plant in bloom. Look for a plant has healthy foliage and roots that almost fill the pot. Beware of plants purchased late in the season, as they may be seconds or leftovers from the bare root season that have been potted. Roses purchased at the end of the summer may have been stressed by heat and are best avoided.