Every November we get the same calls: damp patches on bedroom ceilings and water pouring down walls. Nine times out of ten the cause isn't the roof — it's gutters full of leaf mulch that's been rotting since October.
Here's the check we run on every property: clear gutters and check they sit at the right fall (water should run to the downpipe, not pond); check joints for drips while water's running; look up at fascias for staining that marks overflow; make sure downpipes run free all the way to the drain; and check valley gutters on the roof itself, which fill with leaves faster than anything.
If you're not happy on a ladder, don't do it — falls from ladders are still the biggest DIY killer. A gutter clear costs far less than the damp damage a blocked one causes.