http://www.quiltingboard.com/t-112333-1.htm to see pictures on pp. 1 & 2
I had been using a plexiglass extension for my machine, but the heavier projects had a tendency to cause the extension to slide around and move.
I started looking for tables that the machine sat down in and created a flat working surface. But, boy are those things pricey.
I decided to try and built one myself. Went to Home Depot, bought 1 8ft 2x4, 2 8ft 1x6 and a 2ftx4ft piece
I would never do them that way. You end up with bias edges on all the edges. Cut the squares bigger, draw the line down the center and sew a quarter inch away and then trim them down. The rule is to add 7/8ths of an inch but you can add an inch or even an inch and a quarter and the square them up to perfect.
Buy this, you'll never regret it, from Bear Paw Productions. She's wonderful to deal with.