My 7 year old son's floor is always completely covered in Lego, so I'm not sure why I didn't do this earlier. It was so quick and easy. I'm hoping it will help with keeping the floor in a more manageable condition.
I have used an old Where's Wally quilt cover and some denim given to me by my Mum to make the mat. The quilt cover has already been used for a couple of bags and a few pairs of little people pants, including these reversible pants http://365crafty.blogspot.com.au/2012/04/day-40-reversible-baby-pants-from-doona.html