[DefaultMemberAttribute("Item")] 
[SerializableAttribute()] 
public class PropertyProductRelationCollection : System.Collections.ObjectModel.Collection<PropertyProductRelation> 

class MyPage : System.Web.UI.Page
{
    public void RenderGroupFields(Dynamicweb.eCommerce.Products.PropertyProductRelationCollection propertyRelations, Dynamicweb.Rendering.Template ParentTemplate, string LoopName)
    {
        if (propertyRelations.Count > 0)
        {
            Dynamicweb.eCommerce.Products.Product prod = Dynamicweb.eCommerce.Products.Product.Create(propertyRelations.get_Item(0).ProductID);
            Dynamicweb.eCommerce.Products.PropertyTypeCollection Types = Dynamicweb.eCommerce.Products.PropertyType.getPropertyTypes(prod, false);

            //"GroupFields"
            RenderGroupFieldsValues(Types, ParentTemplate);
            RenderGroupFieldTypes(Types, ParentTemplate, LoopName);
        }
    }

    private void RenderGroupFieldsValues(Dynamicweb.eCommerce.Products.PropertyTypeCollection Types, Dynamicweb.Rendering.Template ParentTemplate)
    {
        //TODO: insert your code here
    }
    private void RenderGroupFieldTypes(Dynamicweb.eCommerce.Products.PropertyTypeCollection Types, Dynamicweb.Rendering.Template ParentTemplate, string LoopName)
    {
        //TODO: insert your code here
    }
}