GridTrigger.cs

using UnityEngine;
using System.Collections;

public class gridTrigger : MonoBehaviour {

    Collider collider;
    bool isColliding = false;

    // Use this for initialization
    void Start () {
        collider = null;
    }

    void OnTriggerEnter(Collider other) {
        collider = other;
        isColliding = true;
    }

    void OnTriggerExit(Collider other) {
        isColliding = false;
    }
    // Update is called once per frame
    void Update () {

    }

    // Check is grid cube free to use / does it overlap with specific object
    public bool isTriggered (GameObject isInTrigger){
        bool localBool = false;
        if(collider != null){
            if(isInTrigger == null){
                localBool = true;
            }
            if(collider == isInTrigger.collider){
                localBool = true;
            }
            if (collider == null){
                localBool = false;
            }
        }
        return localBool;
    }
}