Just finished my DIY skateboard dolly. It measures 29.5" x 36".
It rides on 12 skateboard wheels that are built to run on standard 24.4" wide track.The frame is two 3/4" plywood sheets screwed together to make a robust 1.5" base. It's stained with IKEA black stain.
I originally used walmart skateboard wheels (4 for $5, cheap!) but they were just too bumpy. Even on the track it was just unusable. These things are so sensitive, that a blade of grass on the track can ruin a shot...Real skateboard wheels are expensive, so I saved my favor for a secret santa who just happens to own a skateboard shop in Louisville. (woohoo!) Real wheels and bearings make *such* a difference! I had to add like 60 spacers to make the newer, bigger wheels fit, but now it's smooth as glass.
It's also much lighter than the MSE Doorway dolly I have access to. (try lugging that thing up a hillside or getting it on a roof top!)
Since these photos were taken I have added black handles inline with the wheels, it makes carrying much easier.