1. 1 10 ft section of 1 inch PVC pipe
2. 4 45 degree angles for PVC
3. 1 piece of 3/4 inch plywood sized for your laptop
4. 1 piece 3/4 x 1 inch wood as long as your plywood is wide
5. PVC glue
6. 6 1 inch drywall screws
Drill bits and screw bits
Pencil and permanent marker
Step 1: Design your desk to fit your bike
On my bike there is a bar that wraps around the back of the seat to form handles that you can hold on to while you exercise. The handles are a little less than 1 inch in diameter and the end sections are about 5 inches long (see photos). This design made it easy for me to attach the desk to my bike by simply slipping 1 inch PVC over the existing handles.
If your bike does not have a handy attachment point you could design your desk to be free-standing or such that it attaches to the bike in some other fashion (maybe with screws or clamps?).