As usual, click any photo to bring up a larger version.
Mix Well. Wait 3-5 days, depending on how cold things are.
Add some skates, serve to your kids, and enjoy.
I picked up eight 2x8x8' boards, and two 2x8x10' boards to frame my rink. This gave us a rink of about 14x26'. This is a bit on the small side for adults, but big enough for kids. It is also the largest that I could fit in the flat part of my backyard.
If your yard is exceptionally flat, you could probably get away with 2x6 boards. This will still give you 4" of ice, plus a bit of room at the top. My yard has a small slope to it, about 1-1/2 to 2" over the width of my rink, but that is enough to make me glad that I paid a few bucks more for 2x8 boards. Not only that, but the 2x8 boards in the store seemed to be of much better quality than the 2x6 boards. Is that because the 2x6 boards are more picked over, or because the 2x8 boards need better/taller/older trees, or just some other reason? I dunno, but generally I suggest you spring for 2x8 boards.
A white tarp is best, as it will reflect the sunlight. A dark blue tarp is probably the worst, as it will absorb light and help melt your rink. You could also just get some heavy plastic. If it isn't big enough, just take it inside where it is warm, and tape it together with clear packing tape. I got that advice from an acquaintance who used to make rinks for his kids. Overlap the plastic by a foot, and tape it on both sides. Should be good enough to hold water long enough for this. You need to do that inside or the tape won't stick!!
I found a 20x28 white tarp, which was close enough to being the right size. Wrap the excess up and over the boards and tuck it underneath. The tarp needs to be about 2' longer than your rink in each direction, so that it can go up and over the boards.
If the ground is solidly frozen, it is possible to just flood the area with water and let it freeze. This saves on the cost of buying a tarp. First you want to pack snow against the boards to help restrain the water. However, on warm sunny winter days, you may just watch your rink gradually melt and run away. A tarp (or plastic) will help retain your water.
Put the boards together with deck screws. 2-1/2 to 3" recommended. My rink was small enough that I didn't bother with stakes. Bigger rinks will need stakes to keep the boards from blowing out from the water pressure.
The first time you fill it, it'll probably take a few days to freeze solid, unless it is exceptionally cold. Two-three inches of water is a lot to freeze. After that, we just kept spraying on a thin later of water each night. We want to build it up to a good 4" thick or more, to help it last as long as possible. Remember to bring your hose inside so it doesn't freeze!!