Where roof slopes meet is called a “valley”, looking at the photo, for obvious reasons. These are often at first floor level or above and so out of sight.
They are a notorious weak point in roof construction. Whether it is due to bad design or later blockage by leaf fall etc, valleys can leak resulting in damp, rot and spoiled decorations inside.
It is worthwhile asking your builder or roofer to take a look every now and then, especially after the winter when the trees have been shedding their leaves. As always, prevention rather than cure.