I wanted a playhouse for my young son to enjoy, but being cheap and having material around I decided to build, rather then buy. I really enjoy the design of the 'Dr. Seuss' style playhouse. This was my inspiration.

Step 1: Conception and Design

I wanted to create a plan using a computer program but because of the irregular design the program could not render a proper image. A rough sketch will do as measurements and angles will be "Good enough, close enough".
While designing this playhouse I could not find a similar model for sale, so for my dimensions i took the average size from a few available playhouses and went from there. 48" x 54" x 50"

Step 2: Construction

I made my base out of 1/2" plywood and 2x4" pressure treated material. One sheet will do for the base, make any size or shape you like. Mine is 4' wide, 6' at the front and 5' at the back. Glue and screw the 2x4" as a perimeter under the plywood and joists at 2' centres.

Step 3: Wall Construction

All wall framing is made of 2x4". I started with the front right corner and made this corner plumb in both directions. I can be a little bit of a perfectionist sometimes so I leveled across the front and installed the front left corner at the same height but at a 10* angle in both planes. The back wall I constructed in the same manner, at different heights and different angles. No angle is greater than 10*.
You will want to add in some extra framing for a door as well. I made mine an irregular shape as well, to keep with the design.

Step 4: Roof Construction

To build the roof, I installed two supports at the end walls. One side I added an extra cut to allow that wall to 'bend'. My roof ridge consists of a single 2x4" with one cut and reassembled to create an 'out of line', wacky roof line. I did this with the top of the wall on the front side so that things did not look too straight. Add rafters as needed. You should have a rafter at each hip and valley(where the cuts are in ridge and wall plates), and recommended not farther than 2'.

Step 5: Sheeting

To sheet the walls and roof I used 1/2" aspenite. It is a crappy building material, but seeing as it was free, it works perfectly. 1/2" plywood would be recommended. Due to the changing and irregular shape of the walls, start in one corner, and work outwards across the sheet. I used screws on everything as they should hold better than nails and you can snug the sheet in better. Use full sheets where possible and install as full sheets. Once the sheet is secured and in its final place trim using a skilsaw along the framing. This way no measuring needs to be done and no funky angles need to be figured out.
The roof sheeting and end wall that 'bends' will need to be sheeted in multiple pieces as one sheet cannot bend in such a manner. Again due to the irregular shape, start in one corner and work out from there. You may have to use more screws closer together and work them in together to pull the sheet in to the framing without popping through the sheeting.

Step 6: Doors and Windows

To add in your doors and windows, once that particular wall is sheeted, draw the shape of your opening on the wall and cut it right out. The cutout will become the door or window. Add on hinges and a handle and this step is done.

Step 7: Trim

To trim the openings and corners of my playhouse I used material on hand that works very well, 1x3" pine. There will be a great deal of trial and error due to the irregular shapes and angles of the roof and walls. Start with under the roof sheeting, next trim out the corners, and last trim along the bottom between the corner trims. Some trims will have to be built in multiple pieces to follow the crooked walls. Some of my trims I had to notch the backsides to allow them to bend as well. Add trim to the inside of the openings as well to create a wider sill and to finish the cut nicely.
More trim will be added later to create a stop and seal for the doors and windows.

Step 8: Paint

Before painting you should seal the joint between the trim and plywood sides. Any water getting in behind the trim will eventually rot out. I used a silicone caulking that will move and stretch with the changing weather. To paint use anything you like that is suitable. We used good ole' Tremclad, lots of colours, it is afterall still a playhouse.

Step 9: Furnishings and Future Expansion

We have added a small play kitchen and a small solar light inside. I will add plumbing later as well if it can be logically included. I have covered the roof in 'ice and water' roll for now but want to use cedar shingles in a pattern to match the house. I also need to create a metal frame to distort the door to match the door frame.

Step 10: Conclusion

Well most of this playhouse was designed as I went along, I definitely had the idea in my head and on paper first, but some things didn't work out on paper, like some of the sheeting. It all works out in the end. I had a great time building this at every step and my little boys love it.
If you have any ideas to add let me know and thanks for looking.