I would like a plan for buying/building a loft bed for a child.

Not just any loft bed. I have found many of those. The Loft Bed Plan
found on Family Fun is pretty close. The plan we have in mind is for a
loft bed that has a decorative panel on half the front and around one
side that looks like a cottage or store front with a window. We want
the loft bed, in the end, to look like a pet store, with shelves and
storage inside for displaying myriad stuffed animals.

As my child grows, I would like these decorative panels to be
removable, as she will outgrow this theme.