As a tree diagram, I'd draw this with 2 branching levels. You obviously have a starting point, which branches into 3 levels for each row of the plan.
Then a second branch level off each of those 3 for the possible outcomes by the columns in that row. So the branch for the top row would have 4 further branches, the second row splits into 2 branches etc.
I'm assuming the probability is based off the area of each box, and that the splits are done equally each time.
As for drawing a maze, it's the same as the tree, just in a bit of a maze sort of shape (corners etc).
P(Y), P(N) and the number of pumpkins should come easily from the tree diagram.
