One of the most successful and beloved canoe designs is a 10.5 foot open canoe called the Wee Lassie (happens to be the first canoe I built) - - so size alone is not the best way to judge. What kind of water he intends to paddle is a more important question, in my mind. All that aside, when using bent ply ribs and other assorted MDF bits and pieces, I would make sure you will be using a good life jacket when you paddle.
Seriously - - with all the work you will put into the boat (at least twice what you expect in advance) - you really should use some materials that have at least a chance at surviving the elements you intend to use the boat in. MDF, with all the varnish and epoxy (expensive) in the world, will not stand up to a wet environment at all. You would be better off using exterior grade ply, although not so pretty.
I am not one to harp on people for not taking my advice - - I just would hate to see you put so much work into a boat and only be able to paddle it once because it fell apart, solely because you used materials not suited to a wet environment (to say nothing about an under water one).
Good Luck and I will be watching how it goes for you.
Russ
PS - - I just thought about it - - you should google "the 6 hour canoe" or the "one sheet ply canoe" or "the lumberyard skiff" and see what you see. I expect you will find a lot to keep you interested.