Placing one object relative to another

I am really struggling with placing objects exactly where I want to relative to other objects. In my game I have a ‘door’ object and I want to spawn a room behind it when the door is clicked on. Each room has 4 exits, one on each side, and I am having a lot of trouble getting the room to spawn with correct orientation in regards to the facing of the door. I was at one point getting it to spawn on-mark, but it had the wrong rotation.

Rooms might not always be the same size, so I need to take collider bounds into account. This basically need to work pretty purely off of the objects positions and orientations with no hard-coding of offsets. A final adjustment can be made in the code spawning the room type but that has to be known ahead of time and work for every case (such as adding in a -y coordinate for basement rooms, etc). Sorry for all these odd requirements but it really is what I’m after.

I created the following as a test. When the cube on the left has no rotation the blocks will line up center to center as expected. (though it says floor I do mean ‘center’ as in a correct sideways T shape) However when the first (left) cube is rotated the positions are maligned.

What code can I use to place the second cube correctly? Any help with code or prefab construction tips is greatly appreciated. Having a lot of difficulty fully and completely understanding how object placement works. I feel like this should be easier and that I’m missing something.

Thank you!!!

using UnityEngine;
using System.Collections;

public class NewBehaviourScript : MonoBehaviour {

	// Use this for initialization
	void Start () {



  public void doStuff() {

    GameObject nextRoom = (GameObject)Instantiate(Resources.Load("vectortests/Floor"));
    //now that position needs to be offset by half the room size
    Vector3 newRoomSize = nextRoom.transform.GetComponent<Collider>().bounds.size;
    Vector3 newRoomOffset = newRoomSize *= 0.5f;
    Debug.Log("Position before halved room offset is added: " + gameObject.transform.position);
    //now add that offset to the position
    Vector3 newRoomPos = gameObject.transform.position + newRoomOffset;
    Debug.Log("Position after halved room offset is added: " + newRoomPos);

    //now that has to be multiplied by the vector
    Vector3 doorForward = gameObject.transform.forward;

    Debug.Log("Forward is found to be: " + doorForward);

    newRoomPos = Vector3.Scale(newRoomPos, doorForward);
    Debug.Log("Final Position: " + newRoomPos);

    nextRoom.transform.position = newRoomPos;

    nextRoom.transform.rotation = gameObject.transform.rotation;

I am an idiot

the prefabs just have to be set up right with parents in the right place there’s nothing at all wrong with

GameObject nextRoom = (GameObject)Instantiate(Resources.Load("Room"));
nextRoom.transform.position = gameObject.transform.position;
nextRoom.transform.rotation = gameObject.transform.rotation;