Building a treadmill desk

[Cadaverous Pallor]

I've found acrylic sheets at my local Home Depot.

As for attaching the desk to the arms - how about just having the front supports shaped similarly to the cardboard mock-up and have it rest on the arms?

In fact - couldn't you get away without bolting anything?

If the acrylic doesn't work out and you wouldn't be able to see the controls, I recommend taking a good photo of the control panel before covering it up so you can navigate it later without seeing it.