well, i havn't started yet as i havnt headed back to the flat lands yet but.... so far, the alterations i'd planned were: in the A frames, not latticing the beams like this guy has, if the wood can sit flush, it should be a much stronger, so an offcut could sit in the gap rather than just laying the beams over eachother... not sure if that makes sense. or not, pictures would be easier.
next, also regarding the aframes, more coach bolts at each join would be required.
the board itself, instead of just being a square with the ply bolted to the front will have more cross bracing.
off he top of my head, thats i all i can rememeber (im not home at the moment so cant get at the drawings) but im hoping that these kinds of things will stop the whole concoction from swaying so much as the one in the video (its on a different video, but its the same guy)
oh and, mines going to be a little higher than this guys.
i'd like to say i hope all that helped, but... i dont think it was that helpful
but i'll be building it in two weeks or so, so pictures will follow if you feel like waiting that long... might be worth it to see where i go wrong.