I built one of these for free today, here's how. I took a 4 foot long 8" diameter log and threw it on the ground. Then I took some smaller logs and split them into 4 wedge shaped peices with an axe. Then I put the wedges under the ends of the 4 ft log on either side chocking it into place. Then I kicked it and jumped on it and it was solid so good to go.
If anyone, like myself, has been a skeptic as to whether this is A)a good way to gain confindence getting onto rails during your off season, or B)a fucking rediculously difficult workout, then you can put that shit to bed because this is both.
I'm in good shape and this shit had me panting and sitting down and my feet muscles (which I didn't even know feet had) were screaming and it was also pretty fucking fun.
So if you were on the fence about wanting to make one of these, as a former skeptic, I would recommend it.