Garage roof advice needed

collingbone614

Our garage roof is flat and over the years has bowed in due to rainwater sitting on it. We want to get a pitched roof put on it so that the rain drains off. It's a detached garage and the roof measurements are approximately 17ft long by 11ft wide. We will also want a gutter and drain pipe putting on.

So far we've received two quotes, one of £1200, another of £1400.

I didn't ask what these included, unfortunately, so I don't know whether there would be a difference in materials involved.

My questions are:

• Would the usual approach just be to build a pitched roof on top of the existing roof, without removing it?
• What materials are usually used for the surface? I've had some talk of using a kind of rubber-based material, others have talked about felt. What are the main differences? I'd appreciate any thoughts on the relative advantages and disadvantages of each.
• What type of wood should be used for the structure of the pitched roof? Marine plywood has been mentioned, is this the usual choice? Any thoughts on this would be welcome.
• Any other relevant thoughts welcome.

Thanks,