A coworker's daughters were quickly outgrowing their commercially available backyard plastic playhouse. He asked me to design a bigger replacement - something he'd build himself. The only requirement was that it be less than 8' in all dimensions.
The result was a simple gabled box 6'x6', 8' tall. Two of its adjacent sides have one foot bays, one of which extends another foot to form a "porch".
A few months after he finished building it, he sold his home. His daughters' affection for the playhouse, and his own sweat equity motivated him enough to rent a crane and truck large enough to move it to the backyard of their new home.