How to create round buttons

Hello! I am creating buttons dynamically. I need to create N round buttons. Window backround is gradient. Amount of buttons can be changed.

Now I am doing it like this:

Button btn = new Button (this);
btn.SetBackgroundResource (Resource.Drawable.myButton);

Where myButton is square picture of my button. First problem : button has not round shape. Second prblem : because of gradient background it looks terribly.