Sorry, no plans.
I had one built, it looked similar to:
The entire things was 8' x 8'.
The window had a bit of a ledge so the kids could use it as a puppet theater. It had a door with a door knob so children who had it as an IEP goal could open and close a door knob (our district is filled with handicapped accessible handles.
The upstairs had a bit of a sunken living room feel. I built it so the kids could sit on the floor (4' x 8' area) and have their feet 6" below their fanny(4' x 8' area).
The upstairs had thick plexiglass on the left end all the way to the ceiling (could be used for window clings, numbers and letters). The upstairs had shelves on one end for books and puzzles. The 'lower' half also had pillows and bean bags. My goal (never got done) was to have a small fold down table so the kids could do puzzles. The second story front was actually all the way to the ceiling. I did not want to have to worry about any monkeys falling.
I built in in the the corner so the other two walls were classroom walls. The down stairs had the 'house center' in it. I had hooks for dress-ups clothing and drawers under the stairs for storage. It would have been nice to incorporate a metal board for magnet play.