Create a blueprint of exactly how you want your windmill to look. The size of your windmill is completely up to you, but be sure that you purchase the correctly rated equipment accordingly. If you have questions about any of the components, ask your local hardware store if that component will work with your layout.
Assemble your windmill body using your blueprint design. Your windmill can either be a simple rectangular box or made fancier by tapering it at the top. Leave the bottom open. Create a false bottom by adding a piece of lumber that just fits inside the structure, if desired. This will be where you can place your transformer so that it will not be exposed directly to the ground.
Drill a hole at the top of one of the sides large enough to fit your electric motor rotor through it. Make sure your rotating motor has a threaded rotor and is rated to the weight of your turbine blades. This is where you will attach your blades. Also, drill a hole or notch in the very bottom on the opposite side.
Connect your electric rotating motor to the transformer. Be sure to follow all of the specifications given by the manufacturer.
Connect your transformer to your solar panel. Be sure to follow all of the specifications given by the manufacturer. Place the transformer on the false bottom in the housing, with the wires traveling outside the housing. Secure the solar panel to the back of the housing, making sure it is not visible from the front.
Secure your rotating motor in the housing so that the rotor protrudes through the hole you drilled previously.
Attach your rotor blades to the rotor. Use the nut to fasten it onto your threaded rotor. Don't torque it too much, just enough to fit the blades snugly to the motor and then give it a 1/4-turn more.
Seal it with the rubber sealant. Make sure to seal every crack that you can, excluding the bottom, so that you can still access it.