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As has been suggested, the length of sun required is determined by where you are growing roses. Here in the mid, Southern California Desert, most roses do quite well with five or six hours of sun. Many do poorly with more due to the extreme heat build up in the foliage and wood, and intense water transpiration rates. I've seen mature bushes literally wilting sitting in saturated rose beds. The sun and temperature were honestly too hot, causing them to "sweat" more water than they cold absorb.
From experience, those which tolerate more heat/sun intensity tend to be more modern, such as floribundas and hybrid teas. They also tend to be ligher colors, which shouldn't be a surprise. Darker colors absorb more heat, causing them to burn faster. Lighter colors reflect that heat. The more heat resistant ones also tend to have shorter petals. Longer petals, like larger foliage, tend to suffer from greater heat build up than smaller/shorter ones. These aren't absolutes. As Ralph Moore has told me for years, "just when you think you know the rules, the rose goes and changes them!" To that, I would add, "Roses can't read!", so what you read of others' experiences won't necessarily hold true for you, in your garden. It honestly boils down to the variables of quality of drainage; quantity of water and moisture retention of your soil; prevailing humidity; speed of winds and exposure to them; proximity to hardscape; intensity of heat and light and probably a few more I am not thinking of at this moment.
The closer to a wall, pavement, etc., the plants are, the hotter the air is going to be surrounding the plants. There is an extreme difference between the temperature and humidity of the air surrounding a rose bush in the middle of a lawn or rose bed, and the same rose, in the same garden planted next to pavement or close to a wall. You can illustrate this point for yourself very easily. The next time you experience a scorching day, after the sun goes down, walk past a concrete block wall and notice how uncomfortably hot the air is the closer you get to the wall. Thermal masses are used and have been for a few centuries, to grow plants not suited for climates and exposures. In Britain and nothern climates, frost tender, or more heat requiring plants are often grown on warm walls to enable them to be successfully grown at all. Here in the desert, we must take great care placing climbing plants on walls, as well as planting shrubs and hedges close to them due to the intensity of the reflected and radiated heat. It's quite easy here to literally cook plants. Better success is obtained by planting larger specimen in fall so there is more bulk and density to the plant before the high heat hits the next year. More plant mass shades the wall better, reducing the cooking of the plants.
In northern and coastal climates, pots against walls and on pavement, as well as black plastic mulch, are used to increase heat so heat lovers such as tomatoes and strawberries may be successfully grown. In our coastal communities, sugar producing citrus, such as limes, tangeraines and oranges, can produce far tastier fruit if grown in large pots due to the heating of the roots producing more sugar. Try the same thing thirty miles inland, here in the desert, and it's VERY easy to kill the plant out right because the roots of the plant are actually cooked by the radiant heat through the pots. At the beach, you want terra cotta and glazed ceramic to make the plants grow better. Here, you want dense concrete, wood, fiberglass, foam or other materials with greater insulation values or the plants will very likely die from too hot roots. Of course, I'm referring to situations where the sun shines directly on the pots. Those shaded from direct heat of the sun light fair far better than those in direct sun.
Trying to suggest which roses will perform better in high sun and heat without knowing the variables is quite difficult. Many of the ones I've mentioned above affect your roses in the ground, too. Probably the best way to determine what works best in your area is to walk down your neighborhood streets and see which ones seem happy around you in similar situations. Once you have a list of potential varieties, it's a lot easier to figure out others which are similar to them and begin experimenting to see how they work for you. It's honestly a case of "the more you know, the more you realize you don't know".
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