Wouldnt a deliver balcony built into a window be more optimal?
1. At street level it's easy for people outside the house to grab things from it (without having a theft drone, ha ha).
2. In my neighborhood houses often have porch coverings or are too close together for there to be good drone landing places at windows.
3. There are no people to accidentally run into on roofs (usually).
Of course in an apartment complexes and such not everyone has a roof, and people can't just grab stuff outside of the ground floor so a window ledge would make sense.
Probably not one size fits all, really.