Hmm I can only find the one picture
I did this on a SMALLER scale - we bought a normaly play-house and I built the mezzanine because my children are like the Borrowers i.e. very small and those normal playhouses were too big for them.
This is it mid-way through. I basically built a frame which supported the upper floor and made a ladder to go up to it.
To finish it (not in pic) I built a safety rail around the edge using some old clothes rail left over from a wardrobe I had made a few months beforehand. Then I painted the inside of the shed (including the floor) cream, using exterior wood paint. This really lightened it up.
Made a few shelves and put the toy oven etc. in
Lovely jubbly