TermsAgreement.cs

using Sitecore.Form.Core.Attributes;
using Sitecore.Form.Core.Visual;
using Sitecore.Form.Web.UI.Controls;

namespace MyProject.Integration.Wfm
{
	public class TermsAgreement : Checkbox
	{		
		[VisualProperty("Agreement Text:", 200)]
		[VisualFieldType(typeof(TextAreaField))]
		[VisualCategory("Appearance")]
		public string TermsLabel { get; set; }

		public new bool Checked
		{
			get { return base.Checked == "Yes"; }
			set { base.Checked = value.ToString(); }
		}
	}
}