A.) Wait for Windows 10 to release, and then build my new PC. Hardware could change, so I might make adjustments to my part list if this happens.
B.) Get Windows 7/8 and build it NOW, but upgrade to Windows 10 when it releases.
yeah windows 10 will be free for owners of both 7 and 8
so it's really just a question of whether you want to get it now or later. sure you could say that if you wait some better hardware might be released but that will literally always be the case, whether you buy it now or later