If you're planning on a home extension, you're probably more concerned with what's going to be put inside it. However, you should really think about whether you want the roof to be pitched or flat. Due to the expense involved in a home extension, many homeowners simply go for a flat roof. This can be fine, and flat roofs do usually work out to be a lot cheaper, but they don't come with the benefits delivered by a pitched roof.
Here are just four reasons to go with pitched.
Most homes will already have pitched roofs. In such cases, you will almost certainly find that adding a flat roof isn't as aesthetically pleasing. It won't just conflict with the current style of the house – it will also make the extension seem more tacked on. It might take a bit of time for the pitched roof extension to weather enough to look like it was always there, but you'll eventually end up with a roof extension that looks indistinguishable from the rest of the home.
When you go for a flat roof over a pitched roof, you're going to be giving up a certain amount of space. You might think that sloping ceilings aren't great for space since you can't use them for extra rooms. However, you can create a higher ceiling for a more dramatic appearance, or you can use the area for attic space to give you more storage room. Additionally, having more space between the ceiling of a room and the top of the roof outside means having more room for insulation, which is why pitched roofs are generally more energy efficient.
A pitched roof can be slightly harder to clean than a flat roof, but you won't need to clean it nearly as often. The problem is drainage; since flat roofs can trap rainwater instead of running it off, drains can quickly become clogged. As the water runs off a pitched roof, it will sweep away debris with it, but that isn't something that will happen with a flat roof.
Ultimately, the fact that flat roofs tend to collect rainwater, dirt, and debris more easily than pitched roofs usually sees them needing to be replaced after shorter periods. Unfortunately, this can be the case even if you take fastidious care of the roof since a flat surface just isn't as structurally sound as a pitched one, which will distribute weight more evenly.