The base was cut from a pine board 100mm wide, 12mm thick. They were around 160mm long. Narrow strips were cut from the same board to make the side pieces that you can see being glued on in this photo. (Click on the photos for enlargements)
The wheels (more like rollers) were cut from a shovel handle. They were held in place with 1.5″ nails with holes drilled through the center of the wheels a little wider than the nails. The nails heads were glued onto the wood because they became loose after some pushing around the floor. It wasn’t a very good solution but it worked. You can see them in this photo:
Then the body was made from two pieces of the same board glued together. (A single, thicker piece of wood would be simpler if it’s available.) The shape was cut roughly with a saw, then cleaned up with a file.
A single screw through the middle held it onto the base. Not too tight though, to allow it to turn. The gun was made from a strip of the same board, roughly filed round. A hole for it was drilled in the front and it was glued in with pva glue. A small section of the gun was cut off for an antenna mount at the back (short length of wire with a bit of plastic on top). Also, a short section of the spade handle was sawed off and glued on top for the hatch.
After that it was just a matter of painting it:
And these are the two finished ones: