A toolbox is a natural place to start. A simple carpenter's hand tool caddy can be built from plywood. Create low side edges with gable-shaped ends and a thick dowel for a handle for an open-topped tool carrier that can aid in future projects, and be a source of pride. Sand the box well and seal the plywood with a coat or two of water-based polyurethane for a durable finish.
A birdhouse is a natural extension of the carpenter's tool caddy. It is similarly shaped -- just add a roof. Create a hole in the face of the house sized for the type of bird you most want to attract. Typically, 1-1/2 inches is a good size. Seal the house with an exterior latex paint in a bright color or spice it up with a multicolored paint scheme.
Once the toolbox and birdhouse are mastered, the basic box-building skills are in place. Create boxes for items like sporting goods and games that require storage space. Cut your box pieces from dimensional lumber with a handsaw, or have an adult help cut plywood pieces with a circular or table saw for large boxes.
When you're ready for a bigger challenge, take on a doghouse project. The cutout and construction is similar to birdhouse building with thicker plywood. Size the house according to the dog, taking into consideration any growing a young pup is likely to do. Shingle the roof, raise the floor on skids and add a single light bulb for heat to make a cozy canine cottage your dog is sure to love.