Need help with object macro

I am trying to write a macro that will create a slightly oversized rectangle around any given object. It didn't take long for me to run into a wall. The CreateRectangle command requires 4 values. I need my created rectangle to reference the ActiveSelectionRange and add 10mm to the x & y values. I have no idea how to do this. It also needs to inherit the original selection coordinates, centered.

So in the end, if I were to apply the macro to a 10mm diameter circle, it would create a 20 x 20mm rectangle that is centered on the circle. I need a rectangle, so using contours is not viable.

It does not need to inherit fills, outline or colour properties, nothing fancy. Just that.

I'd be grateful for any assistance