The nest-tray ... is in fact a Rubbermaid clear plastic storage box. Since this isn't to be a permanent solution and because we had to get it and 40 lbs of gravel up the side of the building in a swingstage, I went with plastic. Its about 23" long and 15" wide and 6" deep. Long enough for the Trey and Princess (and the chicks as they grow) and deep enough that even 1/2 full of gravel, there is still a bit of protection from the wind.
Holes ... yes, there are holes drilled in the bottom to let the water drain out. And yes the water can come in as well, but we couldn't not put holes in or any water that didn't drain out would be trapped and that would create an unhealthy environment for young chicks.
Gravel ... the rain on June 6th last year was concentrated in about a 5 hour period which isn't usual for anywhere. The drain on the roof works fine for normal rainfalls (like today's) so the gravel in the bottom of the bin (like that better than tray actually) is to lift the birds up out of the water if it should flood like last year. Think fo the gravel as a platform - last year the birds were nesting on sand (basically) that was at most 1/4" deep on the roof. Now the birds are at least 3" above the roof surface, higher if they start rearranging the gravel.
So why not put more gravel in? This ledge is plagued by the wind, by keeping the bin to a certain size and only 1/2 filling it, Trey and Princess would perhaps still be sheltered some from the wind, perhaps better now that their "nest" is smaller and their are walls on all four sides. Also didn't want to have walls that were too low in case Trey (it happens to him more than to Princess) gets flipped off the eggs or chicks. With luck the wall will stop the eggs/chicks from going with him if that happens again this year.
Position on the ledge ... two reasons for this location 1) box too big to fit in corner where eggs were and 2) that corner is way too close to the Big Drop. By moving the box back, hopefully if Trey or Princess do get flipped, and the walls aren't high enough, the chick drops 6 inches rather than 14 stories. Neither is desireable, one is just less desireable than the other. And no, there is no downspout near the ledge, there are no downspouts anywhere externally on the Hotel, so that was one feature we didn't have to plan for.
