[Saadman Mahdi]

Hey, I am no expression expert, but i think this should work out well for what you are trying to do.

1) Add 3 slider controls to your shape layer.
call them,

(i) Slider Control
(ii) Start
(iii) End

Then paste attached code into the scale property.

Animate key frames for the “Slider Control” effect from 0 to 100.

These will be your starting(0) and ending(100) key frames.

The value of control “Start” is the scale at the beginning which i assume you want to be 0, “End” is the value for ending scale which you can change as you please.

slider = effect("Slider Control")("Slider");
linear(slider,0,100,[effect("Start")("Slider"),effect("Start")("Slider")],[effect("End")("Slider"),effect("End")("Slider")]);