Generating platforms one after another

Instantiate the tile at the previous tile position and translate it across half the width.

 //Assign the first tile here.
 Transform lastTile;
 
 //function or coroutine.
 {
     Transform newTile;
     newTile = Instantiate(tilePrefab, lastTile.position, lastTile.rotation);
     newTile.Translate(lastTile.localScale.x / 2, 0, 0);
     lastTile = newTile;
 }