I would screen/mesh under the rafters, so you can still store some stuff up there.Do we screen under the rafters?
Well, you've seen my build.
I wouldn't worry too much about the dust, if you have a dust aversion probably shouldn't have chickens

It does get thick tho, but ventilation is more important IMO.
Ventilating a gambrel roof is tough.
At least this one has taller walls than most.
Is there any opening along the eaves?
One of the best gambrel roof mods I've ever seen:

I know you said you have the rest figured out, but...
How's the floor?
I see some rot on the siding near ground.
Anti-dig apron might be a good a very good idea to keep critters out of coop and out from under coop.
Good examples of apron installation, tho I'd not recommend 1/2" HC...go with 14ga 1x2 or 1x1, will hold up much longer and is easier to lay flat.
http://www.backyardchickens.com/t/1110498/wire-around-coop#post_17093528
https://www.backyardchickens.com/threads/new-coop-project.1169916/page-2#post-18481208