After being addicted to hitting any and all boxes at the park, I decided to build my own box. Finding information on this was a chore in itself, so here is a nice write up to anyone who wants to.
This is for a box the size - 8' long, a little shy of 2' tall and 1' wide.
Costs your looking at - In total I spent $110. $40 for the HDPE(shipped), $15 for the countersinking tool and screws, and $55 in 2x4s,plywood and pvc.
Materials you need(and might want) -
1. A cordless drill will do the job but I prefer to an electric drill with a clutch.(I also used a heavy duty staple gun to make life easier)
2. Countersinking tool you can find at Lowes or Home Depot for around 10 bucks.
3. Enough screws to hold everything together, and smaller screws for the HDPE.
4. I bought 8 8' 2x4's(pressure treated prefered - but costs more)
5. I bought 2 8'x4' sheets of plywood(pressure treated prefered but I skimmed out on this due to I think paint and stain will hold it up enough)
6. Some type of saw to cut everything. I had access to a table saw.
7. Of course you will need the top sheet. HDPE is your best bet. I used 1/4" thick but would like to have used 1/2".
8. Tape measure and angles.
9. 8' long 1" PVC pipes(cheap and easy way instead of using angle iron).
1st you need to find what you want to use for the top layer. I used HDPE(High Density Polyethylene) but understand UMHW(Ultra High Molecular Weight Polyethylene) is the best. Personally I feel HDPE is just fine and less than half the cost of UHMW. At bare minimum you should have at least a 1/4" thick HDPE by 8' long and 1' wide(or the 2'x4' sheet cut in half). Another question I faced is where to find this locally. Well I just couldn't so I settled for buying it from High Density Polyethylene (HDPE) Sheeting | U.S. Plastic Corp.
Start off by cutting all the lengths of wood you need following this general layout. You will need 4, 1' 2x4's cut at 45degree angles. This will give you plenty of support. Do not screw anything down yet, just set it up and make sure everything is nice and even. The height of the 2x4's is 18" tall, 1' long, and of course 4 8 foot long 2x4's.
After your happy with the way you have it set up, its time to screw it down. Once all your 2x4's are properly secure the box might be wobbly and a little unstable. Do not worry about this. The next step is to screw/staple the plywood, and this will make your box rock solid.
As you can see their is a small gap between the top and sides of the plywood. This is a nice spot to put the PVC pipe as it gives it a little more support if you go off the side of your box.
Once the box is all done up in plywood it will be very stable. Now it is time to set up the HDPE. This part is "tricky" but as long as you are careful countersinking the screws you should have no problem.
**NOTE** One thing I wish I did was take a file and file down the edges of the HDPE giving it a slight slant. When boardsliding or going off the edges some of the HDPE comes off on the bottom of my board. It scrapes right off with my fingernail but could be avoided if I filed it down.
Countersinking the HDPE is easy if you bought the 10 dollar tool. It puts the top of the screw under the top of the plastic. Which is why I wanted the 1/2" thick instead of the 1/4" thick HDPE, less to worry about but costs more.
Once you have countersunk the screws and the top sheet is secure properly the last step is to put on the pvc tube. All you need to do is drill a hole a little bigger than the screw itself through 1 side of the PVC. Then screw the pvc into the 2x4. You want the PVC sitting lower than the HDPE so you dont catch it.
Go set up your box where you have a good spot to put it and go have fun!
On a side note - I will be painting the box this spring. I did not have a well ventalated place to paint that was heated and I want it to turn out nice so I will just wait. Also I left the ends open for transportation. I will be sealing them this spring and adding 4 -6 handles. Along with building another 8' box that attaches to this one. 8 feet is a little short but still fun none the less.
Enjoy and I hope this helps.