Tile roof explained

Introduction

Just like any rooftop covering, Roof tiles are designed mainly to keep out the rain.
Traditionally made from locally available materials (terracotta or slate), modern
materials (concrete and plastic) are more commonly used because of the cost factor.

Well maintained slate roof

Rooftop 

Roof tiles are fixed to the roof structure by hanging/staging them and get fixed with nails.
Usually in parallel rows and with upper rows overlapping the lower allowing runoff.
A secondary reason is to cover the nails that hold the lower row.
Where pitches meet one finds roof tiles of special profiles and calls ridge, hip and valley tiles.
These can either be fixed in place with cement mortar or mechanically.

Aesthetics

Tiling has also been used as a protective weather cover and aesthetics for the sides of timber
frame buildings. They are hung to laths (a finishing mainly interior dividing walls and ceilings)
which are nailed to wall timbers. Tiles are then nailed to it via the same overlapping process.
Specially moulded tiles sometimes having a decorative pattern, will cover corners and jambs
(side posts or surfaces of a doorway).

Slate

Slate roof tiles, traditionally very popular in some areas where there was a source of supply,
is now less common because of the cost involved.

Photocells

A company called Tesla, Inc. developed tiles with photocells which, when attached to the roof
and connected, generates electricity to power the property.

Summary

Roof tiles come in many shapes and sizes and made from different materials.
Attached to the roof, it not only has a protective function but also adds to the aesthetic value.
Not being a cheap or easy material to work with makes it costly to install and maintain and is
more often used in an upmarket property. However if properly looked after it will serve you
well for years and is nice to observe.