In this tutorial from the "furniture" series we will model an accurate wooden stool. We won't go and actually change the units setup, but bare in mind that one unit equals one milimeter.
Start by creating in the Top View a Box 290 units long, 290 units wide and 15 units high with 1 segment on each side. Place the box in the center of the grid in the Top View.
Convert it to an Editable Poly (right-click > Convert To: > Convert to Editable Poly) and go to Edge sub-object mode (hotkey: 2). Select the corner edges (you can do that easily in the front or a side view).