gather-and-defend/Assets/Scripts/Drag&Drop/GameObjectPlacementButton.cs

using System.Linq;
using UnityEngine;

public class GameObjectPlacementButton : UnitPlacementButton
{
    [SerializeField]
    private GameObject _prefab;

    protected override bool CanPlace()
    {
        var isBuilding = _prefab.GetComponent<Building>();
        return ResourceManager.Instance.EnoughFor(_rock, _wood, _food, isBuilding ? 0 : GlobalConfig.Instance.Current.populationCostPerUnit) && _button.enabled && _canSpawn;
    }

    protected override DraggablePlaceholder Place()
    {
        var instance = Instantiate(_prefab);

        //we need to fetch the detection size before stripping the object
        var detectComp = _prefab.GetComponentInChildren<Detection>();
        Rect detectionRect = default;
        if(detectComp) detectionRect = _prefab.GetComponentInChildren<Detection>().DetectionRectangle;

        //strip the object
        foreach (var r_body in instance.transform.GetAllComponents<Rigidbody2D>()) 
            Destroy(r_body);
        foreach (var coll in instance.transform.GetAllComponents<Collider2D>()) 
            Destroy(coll);
        foreach (var script in instance.transform.GetAllComponents<MonoBehaviour>()) 
            Destroy(script);

        var placeholder = instance.AddComponent<ObjectPlaceholder>();
        
        placeholder.Prefab = _prefab;

        //assign outline material to all renderers of the placeholder
        foreach (var rend in instance.transform.GetAllComponents<SpriteRenderer>())
        {
            var color = rend.color;
            color.a = 0.6f;
            rend.color = color;

            rend.material = _outlineMaterial;
            placeholder.OutlineRenderers.Add(rend);
        }
        
        CreateRange(placeholder, detectionRect);

        return placeholder;
    }

    void CreateRange(DraggablePlaceholder placeholder, Rect detectionRect)
    {
        if (detectionRect == default) return;

        var detection = new GameObject("Detection");

        var rend = detection.AddComponent<SpriteRenderer>();
        rend.sprite = _detectionRangeSprite;
        rend.sortingLayerName = "Character";
        rend.sortingOrder = 1;
        rend.color = new Color(1, 1, 1, 0.2f);

        detection.transform.SetParent(placeholder.transform);
        detection.transform.localPosition = detectionRect.position;
        detection.transform.localScale = detectionRect.size;
    }
}