Selenium: FindsBy with collection

I am a beginner in testing and have a question. How can I correctly use ReadOnlyCollection<IWebElement>if I use attribute FindsBy . My collection is always null after started test. Heres is my code in C#:

        [FindsBy(How = How.Name, Using = "role")]
        public ReadOnlyCollection<IWebElement> radPercentage { get; }

and here is testing web: http://ift.tt/292gZAu

I want to do something like this: radPercentage[2].Click();