You can say, from the context, what's going on here, but it doesn't sound to me as if these were "leaves" "fluttering down", but, rather, "foliage" (still attached to the trees), swaying down over the roofs, somehow.

The foliage, still fresh, swayed [waved, hung] down over the old rooftops, wrapping them with transparent clouds of green.

--------------------------------------------------
Note added at 2 hrs (2008-10-27 21:51:14 GMT)
--------------------------------------------------

Anyway, the image of "leaves" becoming "dusty" sounds very odd in English.