I've designed a simple Vertical Axis Wind Turbine (VAWT) that can be scaled for 3D Printing. I've attached the Solidworks files of the piece-part assembly that can be scaled to your bed size or chopped and manipulated to work with your print area. (You may have to get creative with ways to attach the larger parts back together if you have to print them individually, but a little JB Weld or Epoxy goes a long way, right?)
Besides the plastic needed, you'll need some magnets (I typically use kjmagnetics.com they have great Neodymium products), wire (I recommend enameled magnet wire for the coils, needs to be insulated but the thinner the insulation the better!), a 3phase-DC rectifier (Digikey.com is great for these types of components, make sure to get one that can handle the amperage you're creating! [influenced by magnet size, speed of spin, distance from mags to coils]), and lastly a small bearing of some sort that matches the size of your central shaft). Obviously you'll need some fasteners and/or glue! In the zip file of the parts there is also a simple wiring schematic that I grabbed off Youtube for the stators.
The best way to figure the power you'll make from this is testing! Trial and Error. Start small, see what kind of DC amperage you get per rotational speed (angular velocity for all you engineers out there!) I recommend building the stators and magholder first, putting them on a shaft and spinning by hand to see what kind of amperage your coils create!
My goal here is to offer a simple VAWT design for everyone to build and learn from. The premise is simple, wind speed = rotation = power generation. Beyond that, get creative with the design! These can be made into super efficient generators and gorgeous works of engineering art!