Same happened to me with a house I owned when we replaced the roof. Things I had in the unfinished attic were mostly in boxes, but the dust was easy to remove on most items. Hopefully that’s true for you too.

I’d show your landlord, do your best to clean it all, then if any items need extra cleaning, talk about the bill for those. Of course, you’ll also want to know if you had permission to store items in the attic. I’m assuming your landlord knew about it, but if use of the attic isn’t explicitly part of your lease, you may have trouble demanding anything.

Hopefully it’s not a big deal in the end!