Is that window a double hung? If so I would imagine you can remove both top and bottom sash from the window to make it a lot easier to access the roof.
Almost all modern double hung windows have removeable sashes, just tilt the window in like you would to clean the outside then raise one side where it pivots in the window track up while leaving the otherside still. It will allow the window to come out of the track and then you can set it down and out of the way.
This is at least the case with every modern DH window I have installed or dealt with. Some are more of a hassle then others but they all can easily be removed.