Why do you need a treadmill desk? The question should really be: “Why don’t you already have one?!”
With one, you can walk gently while you work, and the benefits of doing so are well documented:
"According to a study by James Levine at the Mayo Clinic, users can burn an estimated 100-130 calories per hour at speeds slower than 2 miles per hour ... Recent studies suggest that prolonged sitting is linked to an “increased risk of heart disease, obesity, diabetes, cancer, and even early death" - Source, Wikipedia
Also read this http://www.nytimes.com/2008/09/18/health/nutrition/18fitness.html?_r=0
But treadmill desks are crazy expensive!
If you know you want one, source yourself a cheap second hand or kerbside chuckout treadmill (about 5 weeks after new year is a good time to go kerbside hunting!), and modify it. With the money you save you can have a nice holiday to show off that new body!
This video shows how I made a DIY treadmill desk, which is angle adjustable. Your own treadmill will have a different layout, but I hope this gives you some ideas:
Here’s the design I used. It should be straightforward to follow the principles applied.
The finished product:
Instructions
1. Remove control panel.
Here, it pays to source a cheaper treadmill, as the more expensive ones tend to have busier designs and worse, permanently fixed control panels. You can still make a worthy desk from a treadmill with a fixed control panel, but the table will probably end up blocking the controls
2. Mount blocks onto control panel mount.
If you don’t need the desk to be angle adjustable of course, you can just mount the table directly onto the blocks.
3. The fiddly bit – Mounting the table onto the blocks
Next, you basically have to align the hinges, blocks and tabletop so that the middle block falls freely when the table is raised, and the blocks fall into the correct position that works for you, both when flat and raised. This is probably the most difficult part.
An extra pair of hands is certainly helpful at this stage!
Due to the location of the hinges, it is difficult to screw the hinges onto the mounting blocks/table, as whichever one you do first, the other part is going to get in the way of access to the screw holes. 
I ended up using a side ratchet screwdriver like one of these:
4. Remount the control panel in a convenient location
As can be seen, the control panel is now attached with a custom flexible organic mounting solution – otherwise known as a couple of pieces of scrapwood.
Here a a view of the back with the table raised. Notice the control panel mount on the lower left, screwed into the left hinged block.
All done, let’s go to work … and play!
If you have any comments, or have your own build to share, I’d love to hear from you.
