How do I add a scaled grid to a google map?

I am trying to solve the query below for a colleague. If I have a Google base map and want to draw a grid over the top, with grid squares being 100m x 100m as in the key, how can I do it? Basically, how can I draw a standard sized grid that can then be copied and overlaid on other maps without having to draw each line individually? I have tried Word using a table with the image of the map behind it but adjusting the column widths and height widths requires a lot of tweaking and it is hard to get an accurate grid to scale. Can anyone offer a suggestion? Thanks if you can help

 

I am trying to solve the query below for a colleague. If I have a Google base map and want to draw a grid over the top, with grid squares being 100m x 100m as in the key, how can I do it? Basically, how can I draw a standard sized grid that can then be copied and overlaid on other maps without having to draw each line individually? I have tried Word using a table with the image of the map behind it but adjusting the column widths and height widths requires a lot of tweaking and it is hard to get an accurate grid to scale. Can anyone offer a suggestion? Thanks if you can help