I'm also wondering how you will get the decking up ther on the roof. I pretty much avoid doing two story work like that, but have a few times and hate it. If you have to do it by hand, it's a royal pain.
I have always worked material up from the first floor through the trusses in those situations.
It's always good to have a two-story ladder placed on the outside before you put the last sheet down.
"Live like you'll die tomorrow, but manage your grass like you'll live forever." -S. M. Stirling