Drawing region of acontrol using GraphicsPath

Question

Hi everyone i'm trying to build a control (panel) with specified region. I'm using a GraphicsPath object to draw polygon but it draws nothing. The point i confused is that, it's working if i write;
    panelPath.AddRectangle(..)   or panelPath.AddEllipse(..)   but not working if i write;
    panelPath.AddPolygon(pointArray) or panelPath.AddCurve,AddBezier,AddLines .

My aim is just building a simple panel with round corners, should i use addpolygon or something else , any hints ???