okay this is one way to build a roller coaster box. i find this the easiest way to build it. first get a very very large sheet of wood. and find some material that will form the the shape of the rail.in our case we used a sort of composite decking material it works very well. first set the big board on it's side and get four blocks about two inches wide. screw the first block at the angle and at where you want the rail to start, and put the other blocks at the bottom or at the top of the curve you want. it will help a lot.okay so once you got that you need to trace the line of the rail. then you want to get a saw zall or jig saw. and you want to cut that line.
once you completely cut it you want to attach legs and and cut some little pieces of 2x4 about 2 inches deep. and you want to place a bunch of those along the rim of what you cut. once you do that. set it on it's legs and attach braces.
once you complete that you'll want to lay the top sheet down. we used a composite outdoor decking material. you'll want to start laying it down at the end of the rail, trust me. it's easiest to drill with a bit, then get a counter sicker. and they SLOWLY put in the screws. our top sheet had holes in the core. so screw so that it's just below the surface not any lower. and just start working your way long the rail. once you get that top sheet completely held down. wax the hell out of it. Sam and I also got a blow torch and melted the wax into the sheet. let it sit and your final product should look something like this.
and here's it in use.
hopes this helps.