Consider allowing to increase the width & height after are created the square or rectangle, you can not create form first select the exact size with the mouse (the edges to become editable when you put the mouse over the edges to show an double arrow which to allow to increase or decrease the size and add check-mark who stop the edit and after to can move on the screen your created figure).
To can save as predefined figure to can load in other tab/window!
Scenario: A customer tells you that the distance between the title and the photo is not exactly the same as on his competitor's website and he wants the same distance. If you can save a figure created as a predefined (by giving it a name), you can load the same figure on the other tab/window and to show him if is exactly or not, and you do not have to recreate it again.
To can generate measurable figures in units, for example: create a figure of 24 pixels width and 4.5 pixels of height.