Just create a StringBuilder instance and write the contents of the .VCF to it.
var contact = new GoogleContacts() { ... };
var vcf = new StringBuilder();
vcf.Append("TITLE:" + contact.Title + System.Environment.NewLine);
//...
Afterwards you can save it to a file using the static WriteAllText(...) method of the File type.
var filename = @"C:mycontact.vcf";
File.WriteAllText(filename, vcf.ToString());
Just open a .vcf file with a text editor to explore its contents. Since you only require a couple of properties it should be easy to figure out.
A small example:
BEGIN:VCARD
FN:Mr. John Smith
TITLE:Developer
ORG:Microsoft
BDAY:1979-12-10
VERSION:2.1
END:VCARD
If you want to include an image you have to base 64 encode it.
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