Some great ideas here - reading nook doubles as a bed, ottoman for a friend or book, shelving up top. Maybe the wood for the reading area could be two sets stacked and the padding doubled to make a 'real' bed from time to time? Bed ideas for Ayla.
Tent on top bunk . Source: Delightful Distractions - HOME SWEET HOME. Easy DIY using fabric or even sheets. For bottom, build in rod and use curtain hangers or tack Velcro to wood and panel for a more stationary curtain. For top bunk, hang from ceiling.