EndlessSpace.cs

using UnityEngine;
using System.Collections;

public class EndlessSpace : MonoBehaviour {
	public GameObject tile;
	public GameObject player;

	private float width, height;
	private Vector3 offset, up, right, down, left;

	private void UpdatePositions() {
		var origin = new Vector3(
			Mathf.Round(player.transform.position.x / width) * width,
			Mathf.Round(player.transform.position.y / height) * height,
			0);

		transform.position = origin + offset;
	}

	void Start () {
		offset = transform.position;
		width  = tile.transform.localScale.x;
		height = tile.transform.localScale.y;

		up    = height * Vector3.up;
		right = width * Vector3.right;
		down  = -up;
		left  = -right;

		Vector3[] positions = { Vector3.zero, up, up + right, right,
			down + right, down, down + left, left, up + left };

		foreach (Vector3 position in positions) {
			var obj = (GameObject)Instantiate(tile);
			obj.transform.parent = this.transform;
			obj.transform.position = position;
		}
	}
	
	void Update () {
		UpdatePositions();
	}
}