The most effective way of controlling the heat transfer and make your home more comfortable is roof insulation. 

In order to reduce radiant heat from entering the home in summer, foil faced building blankets and reflective foil sarking are most effective way of roof insulation. Sarking acts like another layer of protection under tiles. Building blanket under metal roof will also help as sound insulation during rain and hail. It reduces condensation on the underside of the roof. Thus, building blanket solves the corrosion problem up to certain extent.
 
To slow the heat transfer into or out of the home by ceiling insulation can save up to 45% electricity consumption of heating or cooling home equipments. Warm air generated by heating systems in winter would be moved towards roof space. If roof is not insulated heat will be transferred out from home and heating equipment has to work continuously to maintain the heat level. Same way during summer time heat of outside the home would be transferred into home through roof, if roof is not fully insulated.