Perhaps the easiest homemade dolly consists of buying or renting a wheelchair that rolls well across a smooth surface. By sitting your cameraman in the wheelchair, smooth camera moves can be created quite easily, as long as you camera operator can hold the camera as steady as possible. One way to ensure the camera stays steady on the wheelchair dolly is to weld a metal plate between the foot rests for a tripod to sit upon; or weld a metal bar with a screw or flat tripod head attached to it to the front edge of the wheelchair seat, so the cameraman sitting in the wheelchair can straddle the tripod and be able to look through the view finder while it is steady. This gives you a way to hold the camera on a stationary object while you move the wheelchair and the shot will have less of a chance of jumping around.
Another option is to take two short sections of PVC pipe and attach two skateboard wheels to the front and back of each. These two short sections with wheels will be the left and right side of your dolly base and should be connected by placing another piece of PVC pipe perpendicular to the sides, creating an H shape. These wheels should be set at an angle when attached to the pipes, so that they will balance and run on another, thicker piece of PVC pipe, which will be your dolly tracks. This base will be wheeled along together as long as the thicker PVC pipe tracks are set about a foot and a half apart, or however wide your H-shaped PVC pipe with wheels on each side is. Because of the angle of the skateboard wheels and the smoothness of the pipe, this section will run smoothly back and forth. On top of this smooth running rig you have just built, you can attach supports for a tripod or for the camera itself. You can purchase all these parts at a local hardware store, generally for under 50 dollars.
A different but effective dolly and steadicam hybrid--which allows the camera to move smoothly in multiple directions--consists of simple materials and a little bit of physics. Take a sturdy piece of wood or a metal rod and attach the camera either directly to it or to it in a protected box or crate, like a milk crate with pillows or padding. The weight of the camera on one end should be balanced out with extra weights on the other end so that the camera will "float" when the support stick or rod is held in the middle. A few people will need to be there to help operate this rig, but it's one of the smoothest homemade dollies or steadicam hybrids that has been used on real professional film sets.