Made from four slotted organizers from IKEA. The bins (also from IKEA) are made to slide into all the nice slots.
The table top is made from a 5' x 5' piece of baltic birch plywood cut to 4' 8". with rounded corners of the top, routed 1/8" edge, and sanded using an orbital sander. Spray paint (first coat is white primer, then royal blue -- which matched the blue LEGO color exactly, and then a clear coat) bought from Home Depot.