Roof nesting oystercatchers

Hi, I have Oystercatchers coming to a flat section of my roof and pecking at window glass (presumably at their reflection). In addition they are coming to the roof daily seemingly just to hang out. The section of roof has a very slight slope to shed surface water off towards the gutter and is covered in a waterproof membrane.

I am considering putting a slightly raised (enough to take it above surface water) tray/platform of gravel on the roof in the hope that they might be encouraged to nest next year.
Is there a minimum gravel surface area they require before a site is considered suitable? What about avian predators - carrion crow and herring & lesser black backed gulls - which are quite numerous?

Any advice would be greatly appreciated, Oyc

  • I have seen them nesting on top of the wall of a friends partly derelict barn for several years on the trot, but here they had some shade and protection from predators. The young when leaving the nest had to jump but that was less than six foot and of course they are very light at that age If they are using the roof as a rest area they may already have nests in the area. What is the reason for encouraging them to nest on the roof where it will be very exposed?