This can be done very simply with a test kit from a garden centre. Dig a small hole at the place where you want to plant the roses. Fill the hole with distilled water, this is neutral. Then stick the point of the tester into the mud for a minute. Take the test strip out, wipe it off and see which value is displayed. To be quite certain, repeat the whole thing at two or three other places nearby.
If you bought bare root roses, then give them water for a whole day so that the roots can fill themselves with water.
Cut the stems to around 20 cm in length before planting. This reduces the area for evaporation and retains the water longer in the body of the plant.
When planting, make a mound around the shoots with a layer of earth of around 15 cm in height, and best of all with bark mulch. Then the young plants are well protected against drying out.
After planting them, generously water the area around them. This will help the roots to bind better and faster with the soil.