What homebrew turbine? If you mean the one here at Otherpower and they specify #17 wire then get as many turns of #16 in as you can, it won't make much difference. At worst it may rob you of a few mA in very low winds and most likely you will more than make it up in higher winds with less stall, a bit more efficiency and less stator heating.
If you are careful with the winding and avoid the waste of space from bringing out the centre turn over the coil and squeeze the coils a bit you may get the same turns.
If you are up in magnet grade you may be better aiming for a few turns less so anything over 120 turns should do.
I use bits of 1/4" wide by .010 thick copper tape to bring the inside leads out and that would give you an extra layer of wire and gain you several turns.
Flux