For this project I used:
2 - 18 x 18 Parsons tables
2 - pieces left over 1/2 plywood
2 - 15 in square lego mats
1 - 14 in drywall mud tray
8 - 2 in L brackets
various wood screws
2 left over pieces of 2 in trim 36 in long.
Cost - most everything was leftover from other projects or given to me. The lego mats were $12 each on sale, the mud tray was $4, the brackets were $6. So $34
Step 1: Clean Up and Join Together
I decided to cut a piece of 1/2 plywood 18 x 36 for the top and then a piece that was 14 x 36 to fit between the legs to go in under the tops. I sandwiched the top between the two pieces of 1/2 inch plywood, gluing it in place. Since I couldn't find my clamps I flipped the tables upside down and set bricks on them. I also added some screws to make sure it was secure.
Step 2: Adding a Shelf
Step 3: Trim on the Top
I was originally going to paint all the added wood to match the table, however, since its a gift for my 8 year old I thought I would let him decide how to decorate the added wood. I did sand it down so there are no rough edges. This way if he wants to draw on it he can, he can add stickers, paint, etc. It's totally up to him.
He loves it and hasn't stopped playing with it since he got it!