I was just thinking about the nest box that was installed in late Oct 2011. They wouldn't be able to see much from that location if it is sitting on a roof floor. It was my understanding that the falcons like to see what is going on outside as far as they could see. It seems to me that they prefer this north location better.....they can see for miles in three directions. 
Actually the roof nestbox is close to the edge of the roof its just hard to see and it's at about the same height as the catwalk on the towers. They've been making scrapes in the box both this year and last, so it is of some interest. And its higher, got more view than the West Winnipeg site and we can't nuke those birds off there!
Technically, every site is different. We know the birds like the catwalks on the towers at this site, but we can't access the catwalks but we can access the roof, so from a project perspective, if we can get the birds interested in a rooftop nestbox that would be a good thing. So the nestbox is within site of the catwalks, about the same height and in a safe location. If they did/do nest on the catwalks, the box is also close enough that if we had to/wanted to move them for safety's sake (remember the last chicks were predated from the catwalk) then we could and the parents wouldn't have any problem making the move.
As for the cubby, it is a decent location though a bit small for growing chicks and it could be a very messy nestsite but hopefully our box design will help reduce that and the risk of bacterial/fungal infections from one year to the next. On the downside the cubby faces north so it is very exposed to bad weather (wind and rain). Wild peregrine nests tend not to be north-facing and in fact recovery project nest siting guidelines were to avoid north facing boxes/sites. However, if that is where they want to nest, we will work to find a way to keep them, their chicks and their nest safe.
