Create a rectangle selection behavior in unity like in strategy games

SelectionSquare.cs

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

namespace Tutorial
{
    public class SelectionSquare : MonoBehaviour
    {
        public Camera Camera;
        [SerializeField]
        private RectTransform rectSquareImage;


        private Vector3 startPos;
        private Vector3 endPos;

        private void Start()
        {
            rectSquareImage.gameObject.SetActive(false);
        }

        private void Update()
        {
            if (Input.GetMouseButtonDown(0))
            {
                RaycastHit hit;

                if (Physics.Raycast(Camera.ScreenPointToRay(Input.mousePosition), out hit, Mathf.Infinity))
                {
                    startPos = hit.point;
                }
            }

            if (Input.GetMouseButtonUp(0))
            {
                rectSquareImage.gameObject.SetActive(false);
            }

            if (Input.GetMouseButton(0))
            {
                if (!rectSquareImage.gameObject.activeInHierarchy)
                {
                    rectSquareImage.gameObject.SetActive(true);
                }

                endPos = Input.mousePosition;

                Vector3 squareStart = Camera.WorldToScreenPoint(startPos);
                squareStart.z = 0f;

                Vector3 centre = (squareStart + endPos) / 2f;

                rectSquareImage.position = centre;

                float sizeX = Mathf.Abs(squareStart.x - endPos.x);
                float sizeY = Mathf.Abs(squareStart.y - endPos.y);

                rectSquareImage.sizeDelta = new Vector2(sizeX, sizeY);
            }
        }



    }
}