Cheap is a relative term so I will start this Instructable with this note. I had a lot of the wood lying around as scrap from other projects and the equivalent whiteboard was between $300 and $500.
I originally was planning to only have one side that can be written on. after some thought I figured why stop with one side when it was just as easy to do two sides.
For the writing surface I used a piece of glass. Both Dry erase and wet erase markers can be used on glass and after a large amount of research this seemed the best economical choice. Some might say the white board paint would be better but what I found is the cheaper paints don't hold up and the more expensive paints cost more than what I paid for the glass. Also if you decide to use the paints you need to make sure that the paint is no older than three months. When looking at the lot numbers and researching the cans at my local stores some were a year to 3 years old. Here is a list of parts I used.
(1) Body Board 3/4" x 42" x 66" MFD
(2) Glass 1/8" x 36" x 60"
(2) Front Plate 3/4" x 5 3/8" x 58" Pine
(4) Leg 3/4" x 4" x 65" Pine
(2) Top 3/4" x 3 3/4" x 66" Pine
(2) Spacer 3/4" x 4" x 24" MFD
(2) Foot 1 1/2" x 5 1/2" x 36" Pine
(4) Right Angle Shelf Brackets 11" x 13" (IKEA)
(4) Caster (IKEA)
All dimensions are finished cut dimensions this can be done with different wood if you have other scrap pieces lying around.
I made it at TechShop
Step 1: Prep the Body Board
Once you have the MFD board cut to size use the shopBot to mill the pocket into the board. If you plan to do a two sided board make sure when flipping the board that the new origin is set correctly so the glass is offset correctly. I left less space at the top an more at the bottom so this was crucial. If you center the glass you won't need to worry about this as much but you might want to adjust the size of the top rail.
Step 2: Paint the Body Board
Step 3: Cut the Frame and Legs
Step 4: Paint the Frame Boards
Step 5: Assemble the Legs
Sandwich a spacer between two legs and crew them together using wood screws. Do this for both legs
Step 6: Place Glass and Hold in Place With Top and Front Plate
If you are only doing one side this step is much easier. I will explain how I assembled the two sided board I made. First get a second person to help you. A piece of glass this large is not easy to handle and if you break it you won't be happy. Luckily mine didn't break. First place the glass in the pocket. Slide both legs in place lining up the edges. Place the top and front plate in position and screw them down and in place. Slide the legs out carefully flip the board over and repeat the process. Once the top and front plates are in position screw down the legs.
One note to keep in mind here. You want to keep the surface under the gals as clean as possible. I ran a shop Vac over mine twice before locking the glass in place.