How about this- instead of using a string like that, why don't you use an array of booleans? (actually integers, since they're smaller...)

int[,] tiles = new int[,]{
    {0,1,1,1,1},
    {0,1,1,1,1},
    {0,1,1,1,1}
};

Then, to instantiate objects over a space, do something like this-

for(int i; i < tiles.GetLength(0); ++i)
{
    for(int j; j < tiles.GetLength(1); ++j)
    {
        if(tileSegments[i,j] != 0)
        {
            Instantiate(obj, new Vector3(i * tileWidth, 0, j * tileHeight), Quaternion.identity);
        }
    }
}

Please note that you can't assign these in the editor, or keep them serialised along with your other properties. You either have to hardcode them, or use a special custom editor.