Inline frame map synced to zoom with shapes?

I have embedded a google map into an inline frame. This was as quick and simple as I thought it would be. The next step I wanted to try, but am short on ideas of if or how it can be done, would be to overlay some shapes (unfilled rectangles) that I would like to size as the user zooms in/out on the google map. I don’t want to use an image for the map (I want the real google map under the rectangles). I was thinking maybe if created my own zoom controls that would drive the google map zoom then I could somehow use those same controls to resize the shapes that overlay the map. Thoughts or suggestions are most welcome.