Pitched roof on single storey extension leaking at low end above patio door

The best thing for you to do is to get a qualified person out to look at the roof. As an example; we would start by checking visibly all of the outer areas of the roof to see if there were any cracked or broken tiles, checking the area where you say the leak is coming from or happening most, remove a layer of tiles to inspect the felt underneath and make sure that the felt is laid properly with the end of the felt rounded into the gutter and not cut short or folded back allowing water to penetrate into the extension. I have personally seen extensions built by builders where felt has been cut short, where there are tiles upside down on the roof and worse where the so called builder has skipped the felt stage totally and plasterboarded inside so it cannot be viewed. If you would like us to come out we do offer a completely free no obligation survey service.

This sounds like either the gutters are blocked; the down pipe is blocked or the joints in the guttering are leaking. From your description the leak is external? I would test this by running a hose into the gutter, stand on a step ladder to watch what happens with the water, it should become apparent quite quickly where the source of the problem lies. If the leak is an internal problem then it could be that the tiles have been incorrectly laid with a poorly fitted underlay. To investigate this fully would mean removing large sections of the roof tiles to expose the problem. If you're able to post a picture it will assist in pointing you in the right direction. Jon