I think you will have about $150 invested in aluminum, skateboard wheels, plywood, and pipe and be very disappointed in the result.
Here is a link that shows a bit more of exactly the same design.
One of the notes at that link says: "Remember, this isn't a professional level dolly so standing or sitting on the platform will most likely destroy it." Of course it is useless if you can't sit or stand on it.
The only thing you could put those PVC rails on is a solid floor or pavement. And they tell you about the need to put some padding on the rails or wheels to cut down vibration.
A real dolly is like a railroad track with strong rails and a decent foundation, like railroad ties, if it is not on pavement.
If you have solid floor or pavement, you would be far better off to put four small wheels with inflatable tires on a cart with a platform big enough to stand or sit on with the camera. Have a handle for someone to pull it (better than pushing). And you don't have to worry about length of rails; you can pull it all the way across the parking lot. You could even tow it with your car.
Here is a design that is easier to build, and will work better:
Plywood deck on frame with 2x4 side rails. The deck is firmly screwed to the frame to make the whole thing rigid. Double thickness 3/4 plywood glued and screwed together would be good if it isn't too heavy to handle.
If I were building it I would make a light weight closed box frame and deck, but I can't try to explain that here. Send me a private message with Email address if you want a sketch.
Wheels mounted on axle shafts through the 2x4 side rails.
Wheel tread width 32 to 36 inches with wheelbase at least 6 ft.
Handle for pulling like your little red wagon.
Probably don't need steering if it is pulled.