There was a super awesome pirate ship at a house near Snow College when I was there. I have wanted something similar ever since. Red Beards Revenge Pirate Ship Playhouse : Luxury Playhouses at PoshTots
Awesome Loft Beds--Since you won't have a window on the one end of your upstairs, this could be a fun idea for the kids area. Not necessarily a bed, but a 'loft' on top of a 'hide-out' area---or something. The bookshelf stairs are a neat idea too.