How to get the height of a tower made out of blocks?

Let's consider a scenario.

I have a box of x = 5, y = 1, z is not relevant to our issue. If I use collider.bounds.extent I get (2.5f,0.5f,z) since those are half of the size. I could also simply store the values in a script.

I am about to give you a solution but you could maybe optimize it and mostly this is for one object, you still to figure it out over the whole game:

Here we go.

1. Get the vertices of the model

2. Convert vertices to world position

3. Find the highest y value of the vertices

4. Use projection to find the vector from the highest point to the ground

5. Get the distance with magnitude.

     Vector3 [] vertices;
        Vector3[] _meshPos;
    
        void Start(){
            Mesh mesh = GetComponent<MeshFilter>().mesh; 
            vertices = mesh.vertices;   // 1
            _meshPos = new Vector3[vertices.Length];
        }
        
        public void Update(){
            // 2
            for(int i = 0; i< vertices.Length;i++){
                _meshPos[i] = transform.TransformPoint(vertices[i]);
            }
                //3
            Vector3 highest = FindHighestPoint(_meshPos);
            // 4
            Vector3 projection = Vector3.Project( -highest, Vector3.down);
                // 5
            float distance = projection.magnitude;
            print (distance);
        }
        
        public Vector3 FindHighestPoint (Vector3[] arr)
        {
            Vector3 highest = Vector3.zero;
            float y = 0;
            foreach (Vector3 vec in arr)
            {    
                if(vec.y > y){
                    
                    y = vec.y;
                    highest = vec;
                }
            }
            return highest;
        }