I think the answer to this problem must be great ventilation and a wildlife garden. i have both and, although Bristol weather has been ideal for aphid proliferation lately, no signs either outdoors or in the conservatory. The roses have good populations of ladybirds on them so they must be finding enough to eat. If yours don't try looking in a conifer tree and carry some to your roses. The bird population is amazing this spring as well and I'm finding broken eggshells beneath the trees as the youngsters hatch out and the parents clean the nests. When ever i go for a walk I keep an eye out for signs of infestations among the native flora but never find any,even in unusual weather like we have just had, so conclude that the tendency for biodiversity i.e. many different plants all growing together, is what keeps the dreaded aphids under control. A mixture of native and garden exotics always looks good and seems the healthiest kind of gardening.
