A skillion roof on a house is a shallow pitched roof usually pitched between 1 - 25 degrees with the lowest point offering the minimal permissible height of approx 2.4 metres.
It's first appearance was seen as a lean to or tool shed roof in an Australian back yard.
The lean to, at the rear of the house was a quick way to cover the outdoor toilet, the housing standard prior to the 1950's, from the elements
A relatively inexpensive construct however all things come at a cost and I'm not necessarily talking about expenditure. No advantage comes without a corresponding disadvantage, just because you don't see it doesn't mean it's not there.
This type of roof is usually constructed with no void so no thermal buffer zone and minimal access for insulation not to mention maintenance or modification.
Areas with this type of roof, requiring venting during summer, and can only be successfully achieved by venting direct to atmosphere, much the same as venting a raked or cathedral ceiling that normally has a higher aspect
Each defined (walled area) needs to be vented independently and can become quite costly.
Venting requires a roof ventilator on the roof with an adjustable type ceiling vent, or register, installed on the underside of the roof ventilator so as to control the velocity of air movement passing through it.
The ceiling vent employed needs to be a highly efficient type that allows a high flow when required and not some questionable plastic product out of a hardware store that works poorly to begin with and not at all when dust gets into the mechanism and breaks as a consequence. Then you end up with a dust trap that continually reminds you of your choice.
Air ingress to this area is critical as the flow could often be high depending on the convection transfer of heat through the roof.
Quality of air is also essential with air ingress via door and windows favouring the southern and eastern side of the area.
If you're going to go the trouble of spending time and money do it properly instead of on the cheap, because it will come back and bite you........at the worst possible time.
As I said 'just because you don't see it doesn't mean it's not there'