starting with the four-squares

I need to find a way to make a shape that selects four of these chips. The shape is like a Tetris piece. Since this only glides around, it can be a 2-D piece. I could simply make a solid shape, but I have two problems with that - first, that it affects the visibility of at least one of the five chips I have already made, and second, that I am having trouble adjusting the opacity, so I can't see the chips fall behind it. (Or the status of the squares it covers, which will also be important.)
The other option is an outline of the shape - I am playing with either a very sharp-cornered shape, like the one at right, or a more rounded one, like the one at left.

In either case, I think they hug the green box a bit much, but I rather thought that shape was a little large, anyway. I'm not really thrilled with either option, so far.

In any case, I am learning more about blender as I experiment with the program. Now if I could just remember how I was able to create a mesh by clicking where I wanted points, rather than adjusting an existing shape....