Source: Creating Custom .NET Controls in C#, http://www.ondotnet.com/pub/a/dotnet/2002/03/18/customcontrols.html

• Create DLL project (.NET 2.0)
• Add necessary References. Under Solutions Explorer, select References > Add Reference > .NET (tab), and select System.Windows.Forms and System.Drawing.
• Add OnPaint() code to new custom control:

  using System.Windows.Forms;
  using System.Drawing;
   
  namespace MyCustomControls {
   
    public class RoundButton : UserControl {
   
      public Color backgroundColor = Color.Blue;
   
      protected override void OnPaint(PaintEventArgs e) 
      {
        Graphics graphics = e.Graphics;
        int penWidth = 4;
        Pen pen = new Pen(Color.Black, 4);
   
        int fontHeight = 10;
        Font font = new Font("Arial", fontHeight);
   
        SolidBrush brush = new SolidBrush(backgroundColor);
        graphics.FillEllipse(brush, 0, 0, Width, Height);
        SolidBrush textBrush = new SolidBrush(Color.Black);
   
        graphics.DrawEllipse(pen, (int) penWidth/2, 
          (int) penWidth/2, Width - penWidth, Height - penWidth);
   
        graphics.DrawString(Text, font, textBrush, penWidth, 
          Height / 2 - fontHeight);
   
      }
    }
  }

• Compile DLL.
• Open Windows Form project.
• Add custom controls to ToolBox palette. Right-click on ToolBox, then Choose Items > .NET Framework Components > Browse (button). Select the custom control DLL created above.
• Go to ToolBox and select the control and place it on a form in the project.