I need a grid of objects at runtime, but the gameObject is instantiated later

I'm building a building grid system for an RTS type game. Currently, I have a grid object with a pool of tile objects, and an array of vectors representing the tile centers. When I begin to place a building, the tiles are moved from the pool to the temporary building, and change their location based on the vector array. I originally tried to instantiate all tiles at the beginning and hide them, but it took far too long to load. The pooling helped solve this, but now I am running into a problem. When my builder builds a building and it cannot be pushed out of the building (something else is in the way) it gets stuck inside the building, so, I wrote a function attempting to find the nearest open tile. Unfortunately, because of my implementation, the nearest open tile is not created yet!

Basically, what I need is to create the tile OBJECTS as in C++ object, so I can still access its functions, but create the GAMEOBJECT for each object as needed so it doesn't lag the game.

Currently I'm trying this:

 private void PopulateMap() {
    map = new Vector3[ResourceManager.MapWidth, ResourceManager.MapHeight];  
    for (int i = 0; i < ResourceManager.MapWidth; ++i)
    {
        for (int j = 0; j < ResourceManager.MapHeight; ++j)
        {
               map[i, j] = GetTileLocation(i, j);
               TileMap[i, j] = new Tile(i, j, this);
        }
    }
}

Will I be able to instantiate a gameobject using this array, and if so, how can I?

Edit: new Tile does not increase the size of the array, so, I now use instantiate but it causes the game to lag after loading.