Roof cleaning is certainly either an easy job to do, nor is it the most enjoyable of the other household jobs.
After the construction of your house the only things people care about is the painting but the most important thing is the cleaning of the roof. The matter that probably appears to be just a little bit of dust on the roof is, mostly lichen and mold growth. This occurs especially in cases of tiled roofing. Both terracotta tiles, and concrete tiles are haven for the growth of mold, as compared to a metal roof, they have uneven surface. Terracotta and concrete tiles have a lot of "nooks" and "crannies" on the surface where fungus and spores can flourish.
The remedy for a soiled roof is "Roof Cleaning" which is a procedure that suits all types of tile roofs. Depending upon what type of roof your house has, its age; it is advised to have your roof cleaned. This would include a high pressure turbo water blast. The places that have more growth of fungi spores, for cleaning those parts you would be requiring an additional mold killing solution to apply to the ceiling before cleaning.
Concrete tiles, when new have a coating of oxide slurry on their surface, and then have a protective glaze spread over it.
This shielding glaze often breaks down slowly over a period due to the continuous exposure to the elements (it mostly takes between 5 to 10 years), leaving the oxide coating exposed. This oxide coating becomes extremely ponderous over years. Pressurized cleaning of your ceiling removals most of this chalky material from your tiles. This process leaves your tiles a little less protected, and they could lose their color absolutely leaving you with a vulnerable roof.
The best solution to this problem is to have your roof completely sealed and properly painted after having it cleaned. This would restore your roof into a better looking one. This adds protection to the roof's surface, preventing any kind of absorption of water during the rains. While with new roofs, it is usually appropriate to have them pressure cleansed, and this would immensely improve the looks of your house.