I have the Fons and Porter one with grids that I hang up. I got it as a gift. It is nice but I wouldn't go out of my way to spend the money for it if I could do something cheaper. I never use the grids and don't think they are all that important. When you put your blocks on the board they are not the size that they will be once they are sewn together so I don't see where the grid helps any.
One suggestion I have however is to make your design board bigger than you think you will need because even then it still won't be big enough!

I have the insulation foam board that is 8 x 4. I covered it with Warm and Natural that I attached with duck tape. I did cut it down to 6 feet tall, but I wish I had left it at 8 feet. It leans against my wall, in front of my closet, in case I need to move it. I works quite well for me. I can stick pins in it if the quilt top gets too heavy, but usually they aren't needed.

Dina

I have done exactly the same thing, with two Fons & Porter design walls and the tiny clear command hooks. They hang next to each other and there is room for all of my ongoing projects.

I just used 1" insulation from Home Depot and cover it with flannel. I had used batting before but flannel is much easier to cleans off all the bits of lint and thread that collect over time.. T pins in the edges works well if you ever have the time or need to wash it. I would hate to live without my design walls and EQ. They both make quilting so much easier. :)

I covered two 8' x 4' insulation boards with felt using a staple gun. I then stapled the covered board to the wall. It is easy to remove and the tiny holes left in the wall are easy to cover with a dab of paint if they do show up. Not having a design wall would be very frustrating for me. Everyone has one wall somewhere in the house that a foam board can be propped up and stored under the bed when not in use.

I too used 2 pieces of 4'x 8' foam insulation form Home Depot and duct taped them together so that the design wall could be folded when not using the full space. My studio is very small and this gives me more options. A friend came over and we gridded the wall with ribbon at 12" intervals and diagonally ... on both the half wall and the full wall. I hold the wall in place with ribbon from eye hooks screwed into the studs of my studio. I also made a vinyl footing to keep the bottom of the wall cleaner and more dust free.

There are a few tutes on the QB about the making of design walls.

My design wall is that blue foam insulation board from Lowes/Home Depot, two 4' x 8' panels covered with flannel, attached to the wall with screws. I have also use Hobbs all cotton batting to cover them in the past.

This might seem a little cheesy to some but I just took a flannel backed tablecloth and used thumbtacks to hang it on the wall in my sewing room flannel side out of course. It works just as we'll as one a friend of mine has that her husband had to construct for her LoL. I always have something on it. The fun part of mine is it is hanging between 2 bookcases and when I need that room for company I just unroll the quilt I have rolled around a long dowel that sits on top of the bookcases and viola a finished quilt hangs in front of whatever I'm working on so the room looks more polished. It's a win win for me as an interior designer.

I covered two 40" x 80" foam boards with white flannel. The Internet suggested a light colored fabric.
They are lightweight and fit nicely behind the door in my sewing room when not in use.
When I need more width, I merely use them side by side. I now wonder how I functioned without them.

My design wall is very portable, removable and can be folded down to a 12" square. All I have are 2 flannel backed tablecloths that I got at the thrift store for 99 cents each. My DH installed 3 hooks at ceiling height on the wall for me to hold 3 clip hangers. I clip the table clothes together with the hangers and hang them on the hooks. I can use one for a smaller project or both for something large. If I want to take them down, I simply unclip them and fold the tablecloths up. The hooks are not noticeable. I have been using the same 2 tablecloths for 3 years and so far they are still working great. Total cost of my design wall? $3.00. I already had the clip hangers. They are the kind you use for skirts or pants.
Oh, and if the project becomes too heavy to stick to the flannel, I can clip it to the hangers themselves rather than the flannel.