For 15 bucks you can just buy the empty box on BrickLink. Here is where you can get it. I think it would be a better use of your time to fork over the 15 USD (plus a few dollars shipping) than to try and recreate the test track. Here is why:
a. the test track is made of a durable cardboard which can withstand an ev3 unit driving over it. Normal paper will likely tear, especially since the test track is shiny and smoother than normal paper. It would be difficult for rubber tires or treads to turn on standard paper.
b. You would have to find the correct size of paper, or worse, connect smaller papers to recreate the track. Of course, it wouldn't have to be perfect, but it does add an extra step.
c. You would have to spend the time coloring. It doesn't sound that bad, but you would need to be very consistent with coloring sections so that the 'color' sensor doesn't have any problems reading the test track.
In short, I think it would be much easier for you to just buy the box rather than try to recreate it.
If you do want to try to recreate it, BrickLink lists the box as having the dimensions 48 x 37.8 x 7.1 cm. Since the box folds out, the surface area of the box will be the dimensions of the test track. (48 + 2(7.1)) x (37.8 + 2(7.1))= 62.2 cm x 52 cm.
The rest would just be a matter of coloring it based on the images.
I hope that helps you out :)