flat metal roofs - ventilate?

I am not sure if this is the right forum but does anyone have any advice about ventilating flat (two degrees) metal roofs. My builder says not to worry that there is plenty of air and there is no need for special vents. At the most he suggests putting in whirlybirds. There is a lot of conflicting material about whether whirlybirds work and we are worried about them becoming noisy or breaking down.I did mention soffit vents etc but he says that this is unnecessary as there lots of ways for air to get in anyway - any thoughts PS we are putting in an indoor pool so there may be a lot of moisture.

Ventilating this space is a good measure to release the trapped warm air. Whirybirds or a ventilated ridge should be used in conjunction with eave vents. The air comes in cool via the eave vents and travels out warm via the ventilated ridge.
Good luck

Do you have any preference as to which way of venting (whirlybird vs vents vs maestro etc) The builder also wants to charge 1300 for two whirlybirds is this reasonable?