I had the same issue, hopefully this will help somebody some day.

//first get all possible mesh renderers

var renderers = gameObject.GetComponentsInParent<Renderer>().ToList();
renderers.AddRange(gameObject.GetComponentsInChildren<Renderer>());

// set the center of initial bounds to the position of the parent object and size to zero, and then encapsulate every mesh

var bounds = new Bounds(transform.position, Vector3.zero);
foreach (var r in renderers)
{
    bounds.Encapsulate(r.bounds);
}

//add the collider to the parent object and set the size and center for the collider, keep in mind the assumption here is that the position of object is 0

var spaceCollider = gameObject.AddComponent<BoxCollider>();
var c = spaceCollider.center;
spaceCollider.center = new Vector3(c.x, c.y + bounds.size.y / 2, c.z);
spaceCollider.size = bounds.size;
spaceCollider.isTrigger = true;

I had the same issue, hopefully, this will help somebody someday.

First, get all possible mesh renderers:

var renderers = gameObject.GetComponentsInParent<Renderer>().ToList();
renderers.AddRange(gameObject.GetComponentsInChildren<Renderer>());

Set the center of initial bounds to the position of the parent object and size to zero, and then encapsulate every mesh:

var bounds = new Bounds(transform.position, Vector3.zero);
foreach (var r in renderers)
{
    bounds.Encapsulate(r.bounds);
}

Add the collider to the parent object and set the size and center for the collider, keep in mind the assumption here is that the position of the object is 0:

var spaceCollider = gameObject.AddComponent<BoxCollider>();
var c = spaceCollider.center;
spaceCollider.center = new Vector3(c.x, c.y + bounds.size.y / 2, c.z);
spaceCollider.size = bounds.size;
spaceCollider.isTrigger = true;

I had the same issue, hopefully this will help somebody some day.

//first get all possible mesh renderers

var renderers = gameObject.GetComponentsInParent<Renderer>().ToList();
renderers.AddRange(gameObject.GetComponentsInChildren<Renderer>());

// set the center of the bounds to the position of the parent object and size to zero, and then encapsulate every mesh

var bounds = new Bounds(transform.position, Vector3.zero);
foreach (var r in renderers)
{
    bounds.Encapsulate(r.bounds);
}

//add the collider to the parent object and set the size and center for the collider, keep in mind the assumption here is that the position of object is 0

var spaceCollider = gameObject.AddComponent<BoxCollider>();
var c = spaceCollider.center;
spaceCollider.center = new Vector3(c.x, c.y + bounds.size.y / 2, c.z);
spaceCollider.size = bounds.size;
spaceCollider.isTrigger = true;

I had the same issue, hopefully this will help somebody some day.

//first get all possible mesh renderers

var renderers = gameObject.GetComponentsInParent<Renderer>().ToList();
renderers.AddRange(gameObject.GetComponentsInChildren<Renderer>());

// set the center of initial bounds to the position of the parent object and size to zero, and then encapsulate every mesh

var bounds = new Bounds(transform.position, Vector3.zero);
foreach (var r in renderers)
{
    bounds.Encapsulate(r.bounds);
}

//add the collider to the parent object and set the size and center for the collider, keep in mind the assumption here is that the position of object is 0

var spaceCollider = gameObject.AddComponent<BoxCollider>();
var c = spaceCollider.center;
spaceCollider.center = new Vector3(c.x, c.y + bounds.size.y / 2, c.z);
spaceCollider.size = bounds.size;
spaceCollider.isTrigger = true;