A lot of roses stop flowering, or the blooms diminish in size during the heat of the summer.
I have a small garden, so I only grow a few roses. Of those, the ones which seem to be unaffected by the heat are;
Abraham Darby. No difference in the size of the flower at all.
Teasing Georgia. This rose never takes a break in the summer.
Blush Noisette. Always producing fresh panicles of blooms.
Perdita. Another rose that always looks fresh.
William Shakespeare 2000. He is happy, as long as he is in the shade.
Aimee Vibert. This year she started flowering in May and shows no signs of stopping.
Marechal Niel. He is not flowering as much as in spring, but a rough count gave me over 50 blooms this week.
Lady Emma Hamilton. This rose blooms all winter as well as all summer!
Buff Beauty. Another one that just keeps on producing loads of blooms.
Daisy