public interface ISiteMetadataField
{
    string Name { get; set; }

    string Value { get; set; }
}

public class SiteMetadataField : ISiteMetadataField
{
    private string _name;
    private string _Value;


    public string Name
    {
        get { return _name; }
        set { _name = value; }
    }
    public string Value
    {
        get { return _Value; }
        set { _Value = value; }
    }

}

private Web UpdateTextField(Web web, ISiteMetadataField siteMetaDataItem)
{
 web.SetPropertyBagValue(siteMetaDataItem.Name,
 Convert.ToString(siteMetaDataItem.Value));
 return web;
}