The easily available size is 8ft by 4ft (2.4m x 1.2m). If you could use all the plywood, this would result in a 13.5 x 6.8 cell maze.
Apparently plywood is made in other sizes such as 10ft by 5ft (3.05m x 1.52m) which is enough for a 16.9 x 8.5 cell maze but it was not available. I did find 5ft x 5ft sheets but I decided not to go with the 5ft x 5ft sheets because they were hard to get, would still be hard to move around and I wanted a few more cells than the 8 cells provided by the 5ft sheets. For reference, the 5ft sheets are called marine plywood.
This all meant that I would have to deal with joints in the plywood and would need a way to minimize the step at the joints.
After looking at a few different maze layouts, given my space constraint, I ended up with the following layout:
If you label the three sections, from left to right, A, B, C, you can put them together as shown to create a 13 x 6 cell maze. If you put two of them together (because they are symmetrical), you end up with a 13 x 13 cell maze.
More interestingly, you can combine A, B, C in other ways to make an “L” shaped maze which happens to fit my work space better and I can end up with an 8 x 11 cell maze or 9 x 10 cell maze.