Goodness, Belgium's climate sounds a lot like central Texas--hot dry summers, coldish winters!
We have quite a few roses spread around the flower beds, and we've found that own-root roses (not grafted) do best for us. We have antique roses, David Austin roses, and bred roses that are still own-root. We plant in the early fall when daytime temperatures are in the 80's, and nighttime in the 60's. We can also plant in the spring--late February or early March--when the daytime temperatures are in the high 60's to low 70's, and nighttime are in the 50's.
Caring for own-root roses means pruning them when they start their new growth in the spring, fertilizing at the same time, and if you have a serious drought, watering deeply once a week. Otherwise, they don't need much care.
The photo is of an antique rose--the bush is about 3 feet tall and five feet wide, and that's after a hard pruning in spring!