Sent by Robin
Editor: How exciting for Gunnar! One thing we'd recommend is checking out Andrew's playhouse - lots of inspiration here! Readers, what things would a 2-year-old love in a playhouse?
• Got a question? Email yours with pic attachments here (those with pics get answered first)
100 DIY Ideas for the 3-Day Weekend
Danielle's Charming, Classic Walk-Up
Good Food to Share 
The Big Book of Small, Cool Spaces 
Apartment Therapy Presents 
The Eight-Step Home Cure 
White Enamel Flatwa...
How To Cook Fluffy, Tasty Quinoa
Perfect Summer Cocktail Recipe: Honey Bourbon Lemonade
A "bouldering wall" across the outside? You could install hand and footholds for climbing, just up to a couple feet off the ground, on that outside wall with the window.
Great little space. How about a worktable along one of the walls and a pegboard for play tools? He could noodle with his tools or use the table for arts and crafts. A play kitchen would be great too. Have you considered dry walling it and painting it his favorite color?
A little table and 2 chairs inside would be fun for pretend snacking and games.
Also I would give him some paint and let him go to town on the inside walls, that would give him a proud sense of ownership.
We just built a tree house in our back yard and I'm trying to get some creative ideas too.
Make a reading nook with pillows and bean bags. Or cover the walls with a mosaic of something like random puzzle pieces or empty egg cartons or something very textural.
Make a musical wall - look here for the idea: http://www.filthwizardry.com/2010/05/music-wall-rip-music-tree.html
I would be tempted to do the ceiling and walls in bead-board paneling and paint it white till you think of something else. It would make it more housey inside, and be quite inexpensive. You might be struck by inspiration from there.
Do you have electrical, maybe an interior and a "porch" light?
They could both be run off an outdoor extension cord.
Certinally more of an expense, but have you considered siding it? I suppose you might want to wait and see if its a house, or a pirate lair, or a saloon... or what? :)
I am currently making a fabric house for my 2 year old. On the front I have put Velcro so I can put different signs up like, Jail, shop, Home.
You could do the same over the door with scraps of wood and hooks.
If you put the peg board at the back you could do a garage sign, tool shop etc etc. For a shop you could hang buckets or use hooks for selling food.
Also when I was young my dad built me a house and put a small veggie plot next to it and gave me plant pots for flowers that I had to look after.
We grew strawberries and easy things like tomatoes