Hi Fahim,
If your intention is to draw rectangle on the diagram then you have to use the following code snippet
Syncfusion.Windows.Forms.Diagram.Rectangle nodeRect = new Syncfusion.Windows.Forms.Diagram.Rectangle(50, 100, 125, 75);
nodeRect.FillStyle.Color = Color.FromArgb(255, 223, 189);
nodeRect.LineStyle.LineColor = Color.Orange;
Syncfusion.Windows.Forms.Diagram.Label lbl = new Syncfusion.Windows.Forms.Diagram.Label(nodeRect,"Rectangle");
lbl.FontStyle.Size = 12;
lbl.FontStyle.Bold = true;
nodeRect.Labels.Add(lbl);
this.DiagramWebControl1.Model.AppendChild(nodeRect);
I have attached the sample that demonstrates this completely. You can download the sample from the following page.
http://websamples.syncfusion.com/samples/Diagram.Windows/F64323/main.htmPlease refer to the sample and let me know if you have any questions.
Thanks,
Nagaraj