all the solutions are good, but it seems there isn't a solution that is built in within AC's capabilities.
I am thinking now of placing a wish to have a tool or command similar to the section tool in principal. where as you would open up the site plan in a new window. that is really an axonometric top view, with the ability to dimension it, mark it up just like a section & elevation window. and it would also update to the model similar as the section & elevation window.
the main issue of concern would be the graphical representation of certain elements, such as trees for example, would it take the 3d form or the plan form. the same applies for slab hatches I guess.
any ideas?