On my legs, a single layer of ancient mid/heavy weight wool tights over regular shorts is plenty down to the high 30s F (and below that, I don't ride, sorry ). I don't know if anyone makes tights like that any more (they're PI circa 1987, and I know PI doesn't make them any more). Actually they had a natural leather chamois in them originally - when I returned to cycling three years ago I just took the chamois out and wear them over regular shorts now.

In warmer weather I'll either wear knee warmers or over-tights. I wear the same tights for either running or cycling. For me, the chamois stays in place better if the garment ends mid-thigh, so if I want more coverage on my legs I wear over-tights.