There is a large variety in commercial pro-styles. This design was made from some steel and wood that was laying around. This dolly holds a tripod. It has 12 wheels (from inline skates) and runs on 3/4" schedule 20 PVC pipe.
This photo shows the dolly in use - without the top. We pulled some slats from a bed to create a more even surface for the PVC to lay on. Also, grass getting into the wheels is a mess and causes vibration. Also seen in the picture are additional weights - in the form of rail road ties. Two 2.5 gallon water bottles should work just as well (at 7 pounds a gallon that's 35 pounds).
Although there are a number of areas that could be improved on the result is more than adequate for high-school use.
Step 1: Materials
qty 2 ) 24" x 2" angle 1/8" angle iron (cold rolled)
qty 3) 30" x 1.5" steel straps (1/8" thick)
qty 1) 4x4 piece of 1/2" ply
qty 12) inline roller wheel
qty 12) 3/8" NC bolt, spacers, nuts
qty 4) 3/8" NC bolts to hold deck (i tried standard, over-sized, nylox, and jam nuts).
*) wood sealant - rattle can
*) blue lock tight
*) black spray paint (with rust inhibitor) for frame