I would get some great dressers and not worry about the lack of closets

Ikea wardrobes:

Growing up my bedroom was in the attic and it had crawl spaces, but they were for the most part greatly unused, so i suggest try putting in built-in dressers, bookcases in where the extend into the crawl space, i.e. try to retain as much as possible the floor area. But because of the pitch of the roof these may have to be customed made

Here are some great ideas for storage and I am sure one will fit the bill http://www.houzz.com/attic-cupboards.Basically you will come 'inwards" the more space you dedicate to a cupboard or storage.