If you live where the weather is warm all of the time, such as California or Arizona, you can trim rose bushes any time of the year. If you want huge, spectacular roses, you are going to have to be brave, and be prepared to look at stubs for a while every year. You can trim a rose bush like a hedge if you want to, but it will put its energy into the leaves, not much left over for flowers. If you want flowers, you need to cut to stubs. This is how:
What you are looking to create is a "goblet" shape. That is, the branches should rise up from the center and go out gently in three directions. If you don't have three good branches, you will have to trim to just two, like in this picture, or just one, if that's all you have. Never, ever, trim a rose bush all the way to the ground. If you do that, you might as well just dig it up. Roses are grafted to root stock and when you get shoots coming from the roots, you have lost the flowering plant that had been grafted.
I've had the pleasure of watching roses bloom after years of neglect in California, and it's amazing. Rose bushes in California grow like weeds - if you want them to bloom like roses, you gotta be brave, and trim them!