You will need:
A flexible place mat
1/4 yd. fabric
decorative elements if you so choose
First you will need to fold up the bottom of your place mat. ( I used one of the small travel sized wipes container for my measurements.) Also if your place mat needs it, fold the top down and hem it.Then sew up the fold on the 2 ends. Then fold your place mat into thirds and then sew a seam up to the egde of your fold so you have 3 pockets.
Then you will need to make a pocket out of your fabric that will fit on the side of your place mat. I just folded a piece of fabric not quite in half and sewed up the sides. Then then I hemed the top and bottom.
Once you fold it right side out it should look like this.
Then I sewed the pocket onto the left side of the place mat. Then on the right side on the place mat I added a piece of elastic so that it will help keep the diapers in the pocket so they don't fall out. (I forgot to take a picture of this.....let me know if you can't figure it out) Then for the changing pad I cut a waterproof matress pad into 4ths and used a 4th of it as my changing pad. you can also make one out of fabric or use an already existing changing pad. I attached a piece of velrco to the back of mine so I can take it out and wash it as needed.
Then I folded the placemat back into thirds (make sure you put your wipes container and a couple diapers in it for measurements) Once it is in thirds you can make a strap that goes around and holds the whole thing together. I used velcro on the end to attach mine.