If you have a old lowrider bike from the 70s or whenever you are going to have a tough time building the bike unless the frame is in perfect condition.  When I got my first lowrider bike it was from the 70s.  At first it didn`t seem like anything was wrong with it but it was a pain in the ass because all the parts I bought first didn`t fit properly and I had to make custom spacers for everything.  It`s a lot better if you but a new lowrider bike frame because it will help you a lot.