[RKDinOKC]

1.) The roof is not on a house to thermally insulate the house.
2.) The roof is there to keep the precipitation out of the house.
3.) The insulation on the houses ceiling in the attic is what insulates the living area of the house.
4.) The roof is ventilated mainly to let moisture in the attic dry out, but also lets excess heat out.
5.) Insulated roofing tiles only keeps the sun from heating the attic more than ambient temps outside (see #4).
6.) Heating an attic in the winter when snow is on the roof is bad. It causes the melt runoff covered by the snow to pool at the soffits, leak, and rot them. Hence the ventilation.