Birds don't just make nests in trees--they will use porches or roofs as well. Not only will birds leave their droppings all over, they also are carriers of parasites such as worms and mites. It is best if you keep the birds away from your roof and simply admire them from afar.
Cut strips of aluminium foil or cut aluminium pieces from a soda can or an aluminium pie tin.
Tie the aluminium pieces around the edges of your tile roof. Birds won't like the glare from the aluminium and will be deterred from flying under your roof and taking up residence.
Find some fake cat and owl figures and hang them around your tile roof. These animals prey on birds, so their images should frighten birds away. You can hang them between the aluminium strips, if you like.
Crush three chilli peppers in a bowl and one cup of water. Set the bowl in the sun for two days.
Pour the liquid in an empty spray bottle and spray around the perimeter of your tile roof. Birds hate the smell and will stay far away.
Bird spike strips are available that you can attach to the edges of your tile roof. These spike strips are uncomfortable for the birds to sit on, so they won't stick around.