This is a fun way to build a "cheap" raft. It is a fun and easy project and will be a buttload of fun once you are finished with it. You will need materials, though, and they don't come cheaply (namely a dollar). Instead, each item can cost anywhere from 1$ to 20$. Anyway you will need:

                     4straight poles, 6-10 ft. long and 3-4 inches in diameter
                     3 shorter poles of the same diameter
                     At least 200 ft. of 3/16 of an inch rope (or 100 8-10 inch bolts and nuts)
                     At least 9 five-twenty gallon size buckets
                     Planks or boards for the deck
                     Hammer, nails and a pair of scissors

And have lots of fun!!

(P.S. This is a very, very confusing instructable, so feel free to ask questions. Oh, and the idea for the raft is to have the length double the size of the width.)

Step 1: Building the Frame

Lay the end of one of the shorter poles over the end of a longer one and at the right angles and lash them together with the nylon cord or with the bolts (if you don't know what lashing is, look it up on google). Then lay the other end of the shorter pole over the end of a second long pole, and lash them together. Then lash the free ends of the long poles to the shorter ones. In other words, you're going to want to make a rectangle for the frame.

Step 2: The Frame for the Deck

Lash each end of the third shorter pole pole across and over the middle of the two longer poles. Then lash the third and forth long poles between the middle of the three shorter ones cross-ways poles. The distance between these two long poles should be just wider then the narrowest side of one of the empty containers. You should now have a rectangle consisting of four long poles crossed by three shorter ones laid on top of them.

Step 3: Putting the Containers ON

Now lash three of the empty containers at even intervals along the outside of one of the outer long poles. Repeat along the outside of the other long pole, and then again between the two center long poles (you should have used up most of your bolts or rope now).

Step 4: Attach Boards to the Deck

Doesn't the title speak for itself? Do what it says!

Step 5: Test Launch

Launch the raft in shallow water and test its buoyancy - ideally the level of the deck should be 6 inches above the surface of the water when a person is on the raft. If necessary, lash more containers to the long poles. You can get 4-6 containers along each pole, depending if it isn't buoyant enough or if you want more people than yourself on it.