Ideal size for community garden plots

I'm dreaming about starting a community garden.  I'm starting to sketch up layouts and how to include a few sizes of plots along with a secret permaculture element along the sides.

For the beds, I'm thinking about a raised bed made from pine logs, filled with some dirt and compost.  There is plenty of planted pine forestland around here if I can get a load donated I'd be all set.  The logs are normally around 8' long.

So what sizes would be appropriate for plots?  I'm thinking a couple sizes would be desirable.  My garden is pretty big (60x120') so I may be overestimating the size that newer gardeners would be interested in.

I'm personally thinking a "small" plot could be 16' by 16'.  Or 8' by 32'.  And a "big" plot could be 32'x32'.  But I have no idea.

And would rectangles be better than squares?  I'm thinking with an 8' wide bed you could do keyhole access points around the outside and get to it all pretty easily.  But if people are used to rows, the square would give them more options.

My target grower is someone in town that has too much shade or no yard and wants to grow food.  There are lots of weekend lake people around here and it might be a draw for them since they often have full shade and small lots.

My favourite community garden was a 3 x 3 m (~10 x 10') plot. No raised beds, just in the ground, with access to a hose for water. For the first year, 10 x 10 was enough, as it had been neglected the year(s) before i had it and was completely covered in mint and grass. I wished there were mulched or grassed paths between the beds so I didn't worry about stepping on other's beds. Some people had two beds (if there were multiple members of a household, they could each have a bed, and managed to switch to have them next to each other). For me, 2 plots would have been perfect, but I was happy to start with my single plot. A lot of plots(75%) were overgrown/got away from people by the end of the year, even with a single plot.  I liked that they allowed you to have perennials, including small bushes.

Another garden (4x6' raised beds) was better in terms of community spirit (gardeners had a work schedule and were responsible for general chores for 2 weeks/growing season including watering the food bank plots and mulching paths and refilling the central water barrels))  but the plot sizes were way too small and i disliked having to water my garden by carrying buckets of water. I also liked that this garden had a communal tool shed. I also liked that some mulch was provided for gardeners (they put a pile in a corner, then you could carry it yourself). I also liked that they had a pollinator/wildflower garden along one fence (with raspberries!)

Both gardens were fenced, with a combination padlock to keep out "hungry snackers"

Our community garden plot is 20'x20' the garden also offers 10'x10' plots.  They occasionally let someone have 2 20'x20' combined as a single plot for their use.  The common area perimeter is jointly cared for and we have a bunch of grapes, fig trees and a few espalier apples.  I know the city offers a raised bed options that are really tall, more than a typical raised bed that is like 4x8 and they reserve these for disabled gardeners.  I view my community garden as a zone 2 / 3 space even though it is 15-minute walk from the house. It is an integral part of our overall approach to growing our own food.   Community gardens rock, we do a ton of stuff on our own property, but we really enjoy being involved in the local garden with others.

If you are working with beginners it's best to start small and grow out. 5m2  per gardener is plenty for a starter and if they prove themselves they can add a bed the following season.
What's most important is that the group decides:
How to join, how newbies are coached
How to leave
How decisions are made
How conflicts are solved
What's personal and what's communal
Starting a community garden made my bubble explode! I'm now known in town as the garden lady.

Our community plots are 8* 16 I think, but I honestly think thats a little too much. You have to think who you'll be marketing to as such; on one hand, you might have people who have downsized from acres and would love the extra space. on the other, you might have someone who has never done a garden and the extra space would be intimidating. I would suggest making the plots 4' wide and 8' long. This has several advantages: you can reach the center without climbing in, reduces the amount of reaching and stretching. If someone wants more space, they can do two plots (maybe second plots cost less than the first to rent), and rotating plots would be easier to do.  If you had excess plots, a seeding of native flowers or a green manure can keep the plot healthy. Personally, my home plot is 4*8. theoretically, it could produce enough to account for 1/3 of my veggie intake. I don't manage it well enough, but that is the most I have time/energy for. oriented so the long side runs East to West, I have enough room for 8 square feet of tall crops, then 16 of medium height and 8 more of short vegetables.

For these beds that would mean the 8' logs as the long side, then logs cut in half for the short side. minimal waste, plus a way to use undersized logs.
You could also have mixed size plots, in which case I would advise keeping one dimension the same. for example 8*16, 4*8 then maybe 4*4 for mini plots.

Take my advise with a grain of salt though -- I'm from a very suburban area where even mowing the lawn is seen as a monumental task. in a more country place where working in the garden isn't viewed as work people might want much more space.