Building or Buying really depends on how mechanicaly inclined you are and how deep you want to get into it.If you don't like mechanical Work, just buy the Kilo.If you are willing to do the work and to deal with the occasional Problems ,doing your own build is awesome.The money depends on what you want for Parts,but that goes for the Kilo as well.You may find yourself wanting better Parts for it later on as well.You can do a conversion for as little as the Price of a Cog(Suicide hub) or a Trackhub.Just keep in Mind that if you do build ,you're gonna need Tools.