These vehicles are usually based on a conversion of a standard internal combustion engined car. This web site describes my conversion of a 1990 Honda Civic to electric. It took about a year to make the conversion. Many people have built conversions is much less time and lower cost. The job is not difficult for someone who has a basic aptitude with mechanical and electrical things.
Books are available and numerous vendors sell the parts which are needed.
In this site, I describe some of the design considerations and components which went into my electric Honda.