When doing the effects and what not, you will notice that there are sheets labeled SYMBOLS and SYMBOLS FLAT. SYMBOLS is great for things like Table, Book, Chairs, or any other object that has Height. As to SYMBOLS FLAT this is good for things like Magic circles, carpets, sheets of paper, thin books, or any other thing that would be relatively flat to the floor.

As to the grid, my preference (and it's mine, so don;t worry if you don't feel the same), is I like the grid to represent actual flagstones on the floor. So I make the grid lines 0.1 in width, and give them a Bevel effect to make them appear to be separate. I also put my grid much lower in the drawing (higher on the sheet list), so that the grid is below the symbols.

Otherwise, good work.