Complex sentence: Builders can purchase a copy of Microsoft's Windows at an electronics retailer or they can download a distribution of a FOSS operating system such as Solaris 10, GNU/Linux or BSD from the Internet.
Split into simpler sentences: Builders can purchase a copy of Microsoft's Windows or a FOSS OS at an electronics retailer. Or they can download a distribution of a FOSS operating system such as GNU/Linux, BSD, or Solaris 10 from the Internet.