How to construct a basis set?



Dear all CLL netters
 	I am working around to construct a atomic basis set. Anyone has
 information about to construct it from the begining. With begining i means
 to start from the first gaussian function until obtain the complete basis.
 I don`t want to modify a basis. I have some question.
 How are contructed the basis set?
 Is there some method to construct it from cero?
 Where can i get information on how to construct a basis set?
 Thanks to all, I will make a summary of all responses.
 Javier Hernnadez
 javierh "at@at" sinamaica.ciens.luz.ve
 Lab. Quimica Inorganica Teorica
 Facultad de Ciencias
 La Universidad del Zulia
 Marcaibo-Venezuela