Asp.net MVC TextArea

Try this:

 <%=Html.TextAreaFor(
        m => m.Description, 15, 20, 
        new RouteValueDictionary(new { @class = "someClass"}))%>

Edit:
This wont work as far as I know

<%=Html.TextAreaFor(m => m.Description, new { cols = "20", rows = "15" })%>

because of this:

private const int TextAreaRows = 2;
private const int TextAreaColumns = 20;

// ...





     public static string TextArea(
                this HtmlHelper htmlHelper, string name, 
                IDictionary<string, object> htmlAttributes) {
            Dictionary<string, object> implicitAttributes = new Dictionary<string, object>();
            implicitAttributes.Add("rows", TextAreaRows.ToString(CultureInfo.InvariantCulture));
            implicitAttributes.Add("cols", TextAreaColumns.ToString(CultureInfo.InvariantCulture));
            return TextAreaHelper(htmlHelper, name, true /* useViewData */, null /* value */, implicitAttributes, null /* explicitParameters */, htmlAttributes);

}