Let me be sure first… when you say GoDiagram, you mean WinForms? For Web apps, GoJS is the way to go, even if you want to do the server side in C#.
So… assuming WinForms, see Need to build a Theater seating diagram for the theater seater sample. It’s not in the evaluation kit.
And, when I get to work, I think I have a seating chart sample I did for someone a while back…