Custom Sitecore Field to get a dropdown list of Roles

SecurityRoleList.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web.UI.HtmlControls;
using Sitecore.Security.Accounts;
using Control = Sitecore.Web.UI.HtmlControls.Control;

namespace BlackTambourine.Core.SC.FieldType
{
    public class SecurityRoleList : Control
    {
        public IEnumerable<string> Roles()
        {
            return RolesInRolesManager.GetAllRoles(false)
                .Where(x=> x.Name.StartsWith(@"sitecore\My Role Prefix "))
                .Select(y=> y.Name);
        }

        public string InputId
        {
            get { return GetID("input"); }
        }

          protected override void OnLoad(EventArgs e)
        {
            if (!Sitecore.Context.ClientPage.IsEvent)
            {
                var wrapper = new HtmlGenericControl { TagName = "div" };
                wrapper.Attributes["class"] = "wrapper";

                var input = new HtmlGenericControl
                {
                    TagName = "input",
                    ID = InputId
                };

                var listName = "dataList_" + InputId;

                input.Attributes["value"] = Value;
                input.Attributes["name"] = InputId;
                input.Attributes["list"] = listName;
                input.Attributes["style"] = "width:300px;";

                var dataList = new HtmlGenericControl
                {
                    TagName = "datalist",
                    ID = listName
                };


                foreach (var i in Roles())
                {
                    var option = new HtmlGenericControl
                    {
                        TagName = "option"                      
                    };
                    option.Attributes["value"] = i;
                    option.InnerHtml = i;
                    dataList.Controls.Add(option);
                }
                
                wrapper.Controls.Add(input);
                wrapper.Controls.Add(dataList);
                Controls.Add(wrapper);
            }
            else
            {
                var value = Context.Request.Form[InputId] ?? "";
                Sitecore.Context.ClientPage.Modified = Value != value;

                if (value != null && value != Value)
                {
                    Value = value;
                }
            }
            base.OnLoad(e);
        }
    }
}