If you have had an extension built, you might have had a conversation with the construction company about whether or not to have a flat roof installed. What a Roofers Gloucester will tell you, though, is that even though you might assume a flat roof is flat, it still actually has a slight incline.
The reason that no roof is entirely flat is as this would cause havoc with any rain or snow that fell on the roof. Roofs are designed to allow water to gently flow off them and into the guttering that runs along the edges. If a roof was completely flat, the water would pool on the top and would lead to water damage occurring. You would find that the water over time would start to seep into the tiles, and you could also find that large amounts of snow would cause the roof to be unstable.
Guttering is placed along the edge of the roof at a lower level than the overall roof structure. This means that the water gently runs off the roof into the guttering, and then this flows along to the downpipe. This downpipe then takes the water down the outside of the house and into the wastewater pipe that then flows into the street.