You want to create shapes comfortably, and all shapes in controlled scale + alignment ?
This new addon let you draw shapes on the grids !!
This tool show grids and you can create well sized shapes.
Grid size can be adjusted easily (Ctrl + scroll mouse wheel).
After all, you can cut into the original mesh or create new face from it.
You can even copy and past the shapes !
Rotation / Move / Flip (horizontal and vertical)
Please find this addon on gumroad ! Thank you