Do you want to complement or contrast your surrounding landscape? If there are trees or scrub surrounding your home, a grey or pale green roof may help the house blend in, whereas a red roof will help it stand out and make it much easier to see.
If you live in a bushfire prone area, you may be required to build your home using materials that have a high fire rating. Non-combustible materials such as concrete and terracotta provide higher protection against radiant heat from bushfires. Tiled roofs pass the requirements of AS3959-2009 for fire zone construction.