In excel if you want to you draw a shape like rectangle more than once, you will have to either repeat the process of drawing the shape or copy paste the previous shape and resize it as per your need
One trick I learnt recently is to right click on the shape you want to draw and then select the Lock Drawing Mode option. With this you can repeatedly draw the shape number of time of different sizes. To return to excel mode press escape.
Update : After selecting the shape if you just click where you want to put the shape, the shape is drawn automatically mostly of 2.54cm x 2.54cm size.