C#.Net and Visio

Question

I'm trying to create a windows application using C#.net and Visio where you can create a map for a plantation. Basically the map will be drawn using squares, triangles, rectangles etc and inside will be circles denoting trees. I want to have the possibility to change the sizes of the shapes in the Basic Shapes window so that the circles will by default be very small. Also I need to be able to name each circle so that when I double click on it I get a window with different values according to the different trees. I'm new to programming but I found MGold's article on Visio and C#.Net useful but I need more specific info. Any help would be most welcome!