Dynamically scale object stacked over another one

Question

I am making a project with three.js where the user can dynamically change the dimensions of the model. The question is very similar to this one that I posted, but I am afraid it is not working since this time I am working with an extrusion of a planar shape. The snippet of the code where I am having problems is the following:

cubeY.onChange(function(value){
     cube.scale.y = value;
     cube.position.y = (cubeHeight * value) / 2;
     roof.position.y = (roofHeight * roof.scale.y) / 2 + cube.position.y * 2 - roofHeight;});;
roofY.onChange(function(value){
    roof.scale.y = value;
    roof.position.y = ((roofHeight * value) + cube.position.y * 2) - value * roofHeight;
});

As you can observe, when I change roof.scale.y, also the object is moving but it should stay fixed to the upper part of the cube. Do you know what am I doing wrong? This is a jsfiddle with the complete code.

Thanks in advance for your answers!

Answer 1

Scaled cube's height is cubeHeight * cube.scale.y and roof's is roofHeight * roof.scale.y.

Top center position of the cube (cube's height) is cube.position.y + cubeHeight/2 * cube.scale.y or just cubeHeight * cube.scale.y

Roof's geometric center is not coordinate system center so it's position is cube's height minus half roof's height

cube.position.y  + cubeHeight/2 * cube.scale.y  - roofHeight/2 * roof.scale.y

Jsfiddle example