Step 1: Materials
Note: I would recommend getting galvanized steel for all parts that will be above ground. Regular black steel will rust within a couple of months unless you paint it often.
The above picture is a spreadsheet of all the parts I used while building the wind turbine itself.
Step 2: The Generator
The generator is the heart of your wind turbine project and it is important to get a good one. What you want to look for is an industrial DC permanent magnet motor. I got mine on eBay for around $65, and it came with a drilled hub meant for attaching wind turbine blades which saved me a bunch of time trying to make one myself.
My motor is rated for 90v DC at 1750 RPM. Using it as a generator, it will do just the opposite, with 80% efficiency. So if I were to spin this motor at 1750 RPM it would produce 72 volts of electricity. Now, I obviously will not be spinning this motor at 1750 RPM, but you get the concept. In order to charge my batteries which are 12 volt deep cycle marine batteries, the generator needs to be producing at least 12 volts. If you do the math, then I would need to spin the motor at a minimum of 233 RPM to charge my batteries.
With my PVC blades, a steady 15 MPH wind will easily spin this turbine at 233+ RPM, allowing my batteries to be charged.