Hi Michael,
Thank you for your interest in Syncfusion Essential Studio.
I have created the sample for your requirement. The sample which I have used it resizes the diagram height based on the Y-Position of the node added at last.For more details please download the sample from below link.
http://files.syncfusion.com/support/Diagram.Windows/Forums/F82352/main.htmRegards,
Gowri