We used MDF, drop-leaf lockable hinges for the leaves, and piano hinges. I wouldn't recommend MDF because it wasn't strong enough for the screws and we ended up having to add bits of plywood to reinforce the areas for the hinges. We also put pegboard on the back to avoid things popping out the other end, and I'm planning on getting some hooks to hang crafty things like scissors and glue guns.
Despite the modifications we had to make, I love my little sewing table! It fits perfectly under our dining room table and but has tons of workspace when it's folded out. Perfect for a small, cramped house! The finished project isn't quite as bright yellow as the flash made it seem, but it is still bright and happy!