Above-ground pools are often forgotten or abandoned and are perfect hosts for organic matter and, consequently, mosquito families. (In-ground pools usually have enough chemicals to deter mosquito breeding, but beware of water accumulating on pool covers!)
Clogged eave about 7 feet off the ground, easily accessible to mosquitoes (they will fly much higher too). The obstruction at the far end (over the downpipe, which should be the low spot unless there is an installation error) needs to be cleared regularly.
Flat roof syndrome. For some reason architects or builders can’t always figure out drainage, or else the roof sags over time. Yes, mosquitoes fly pretty high. If the roof retains water for a week after eggs are laid, the roof is a breeding site!