>How to create a builder for the class

That question is a little beyond what can be addressed in a forum message. I would suggest getting a book that covers builders. One book that has a good chapter on the subject is,

The Fundementals: Building Visual Studio Applications on a Visual ForPro 6.0 Foundation, Whil Hentzen published by Hentzenwerke Publishing ISBN 0-96550-935-4 you can order it at www.hentzenwerke.com